Math is Thematic When You Say “Invariance”

Robert always seems to be obsessing about some aspect of his work, and the last few weeks he has been an absolute veytik in der tokhes because he’s discovered something called “invariance.” He points it out to his students, quizzes his teachers on it, and has taken to philosophizing about it at the dinner table. Even on New Years Eve he couldn’t leave it alone: “You know,” he opined, “I don’t know why we purchased these cruddy plastic champagne ‘glasses’, because the taste of champagne is invariant with respect to the type of container from which it is sipped.” Well, pardon moi! 

But since you’re still reading this, you might as well stick around, because this actually is relevant for your teaching practice, and at worst, it would probably make you seem a lot smarter when talking to your supervisors, colleagues or the people you meet at parties who make snarky remarks about “only being a teacher.” If there’s one thing Robert loves is asking a hot shot attorney, “yeah, well, if you’re so smart, tell me, how would you teach invariance to a 5 year old?” and then watch as he takes a gulp of beer and 23 skidoos towards the corn chips.

Okay, here’s the 411 on “invariance” and why you’re going to see mathematics in a whole new light once you “get it.” Eventually, Robert is going to complete his master opus on this topic and then you can buy it at his store, but for now we’ll just dip our toes in the water and leave you with a few questions. But I’m not going to give you a “textbook definition,” because a) that’s boring, b) that’s not the best way to define a concept. Instead, I’ll give you a few examples, and you can work it out for yourself:

"The number of objects in a group is invariant with respect to the order in which it is counted."

“The number of objects in a group is invariant with respect to the order in which they are counted.”

Now you all know that, because our man Piaget described that as one of the earliest forms of mathematical knowledge children exhibit, and which you’ve no doubt observed time and time again. Invariance shows up over and over again in mathematics education. Here’s another example:

"The sum of two groups of ocelots is invariant with respect to the how the ocelots are distributed between the two groups."

“The sum of two groups of ocelots is invariant with respect to the how the ocelots are distributed between the two groups.”

Are you getting the idea? Basically, the concept of invariance shows up whenever we think to ourselves “it makes no difference if….” Robert loves to use this with his first grades when he hands out materials that comes in different colors. “Okay, these geometric shapes come in red, blue and green, but the underlying function of these materials is invariant with respect to their color,” he’ll say, followed by, “can someone just translate what I just said?” The first time he tried this out, a little girl raised her hand and said, “What that means is that you get what you get and you don’t get upset.”

Less we think that this is just something that shows up in the early childhood years, let’s look at an example from the upper elementary grades:

The area of a parallelogram is invariant with respect to the length of the base and height.

The area of a parallelogram is invariant with respect to the measurement of the base and height.

The above insight came to Robert while observing a student work on one of these cruddy worksheets that a teacher had unfortunately downloaded from the interweb. He asked the student whether it was necessary to re-calculate the area of several triangles which had identical bases and heights, to which she shrugged her shoulders and replied, “I guess so; they’re all different shapes….”

Want to see where this is going in the upper grades? Sure thing: according to Robert, show him a student who is having trouble with solving algebraic equations, and he’ll show you a student who is struggling with the concept of invariance:

The equivalence of an algebraic equation is invariant with respect to whether the two sides have the same amount added or subtracted, or are scaled by the same factor.

The equivalence of an algebraic equation is invariant with respect to whether the two sides have the same amount added or subtracted, or are scaled by the same factor.

If you’ve been following Robert for any amount of time, you’ll know that helping teachers find a “theme” that carries over from year to year is an important aspect of his work (as well as giving young children brain-busting unsolvable problems….) But if you understand even a little bit about these underlying themes, it will make you a better teacher.

Your Assignment: What mathematics topic are you teaching right now to your students? Do you see the concept of invariance showing up in that topic? How would it help your students better understand the mathematics that they’re learning?

This post has been brought to you by SamizdatMath. Yes, we want to sell you stuff, but our stuff doesn’t keep your students’ busy or look cutesy. Our stuff actually makes your kids “think!”

Math Concepts: Why Not Try Teaching Them Sometime? Resources to make teachers smarter and more effective.

Textbooks don’t teach concepts, but if you read this and implement all the techniques, you sure will!


And we’re back: Scholastic’s “Math 180” does a 360…

Loyal readers know that Robert, the originator of this blog and the proprietor of the online store of the same name, has a very low threshold of tolerance for bad mathematical materials. His past posts on this topic, which includes “Why Singapore Math Will Not Put the US at the Top”  and “What Bad Assessment Looks Like, Go Math! Style…”  solidly confirms his status as the top curmudgeon for what he terms “the competition to see who has created the worst math curriculum ever.”

While taking a morning walk along the streets of his Free State of Brooklyn last week, Robert happened upon a brand new sealed and complete set of teaching guides for something called “Math 180”, which the publisher’s website describes as follows:

MATH 180 is designed to address the needs of struggling students in grades 5 and up, and their teachers, equally—building students’ confidence with mathematics and accelerating their progress to algebra.

Word Problem: How many mountains of trees had to be pulped to publish just the teaching guides?

Word Problem: How many mountains of trees had to be pulped to publish just the teaching guides?

I’m going to assume the part about addressing the needs of students AND teachers is an attempt to acknowledge the fact that many teachers of mathematics are unprepared to actually to do their jobs. Mathematics is a technical subject, and unfortunately, many of the teachers who are in the position to educate students in this area are inadequately trained or supported. This is not because they are inept or uncommitted, but because of the low standards of preparation and understanding that we are willing to accept in our schools.

The shameless "experts" who were paid to put their names on this crud.

The shameless “experts” who were paid to put their names on this crud.

So Robert schleps home with this box of teaching manuals, which consists of 6 different thick books, a very retro looking CD (remember those?) AND a thick packet of classroom posters, all of which weighs in at just under a fully loaded Mini Cooper. Opening to the “Math 180 Experts” page, Robert finds the usual gallery of “Lead Authors”, “Advisors,” “Contributors,” and the members of an “Educator Advisory Board,” each of whom was most likely offered a nice chunk of change to act as if any of them had any hand in the creation or production of this scheisse.

Robert was impressed at how the people who actually put together this curriculum worked to check off every kind of educational trend, scattering in references to Carol Dweck’s “growth mindset,” to “Universal Design for Learning,” along with “blended learning,” “formative assessment,” and a host of other educational hot topics that probably stimulate the endocrine glands of people who love this kind of stuff. Don’t get him wrong, Robert adores Carol Dweck, and believes that UDL is good stuff, but if you delve a little deeply, you would see that the actual curriculum violates all the precepts that the aforementioned experts would advocate. Oh, and just to make things they didn’t miss ANYONE, they also listed two “advisors,” as well as one “contributor” from Singapore, because we all know that including that semi-repressive city-state’s name in the context of mathematics education will be just the poke textbook adoption committees need in order to sink massive amounts of public money into this cruddy program.

Once you get past all the marketing materials, you see a pretty dull curriculum which uses all the standard models to remediate middle school students who have either fallen behind or were “turned off” by the mathematics instruction they had before. I was especially impressed by the “relevant” word problems the copy editors included. Check out a few of the following:

Because using the words "email" and "email" in a word problem instantly makes it "relevant."

Because using the words “email” and “video games” in a word problem instantly makes it “relevant.”


If Dave is writing 20+ reviews each week, when will he have the time to do "Math 180?"

If Dave is writing 20+ reviews each week, when will he have the time to do “Math 180?”

Well, we think you get the point: same old “pseudo-content,” same old teacher centered instructivist methodology, same old reward based assessment (you get “badges” if you reach certain levels while using the online learning materials), all gussied up and pre-digested for your use. Okay, we understand that Scholastic, and the marketing agent, Houghton-Mifflin Harcourt YouNameIt, are profit-making concerns and need to return “value” to their shareholders (which probably includes companies like TIAA-CREF, which manages retirement plans for educators), but c’mon, really? You have all these talented authors, advisors, reviewers, copy editors and art directors, and this is the best you can do?

Robert would especially like to castigate the cast of characters who were bought off to put their names and photos in this worthless pile of junk. Okay, we know the teaching profession is not especially well-compensated, but Deborah Ball, you’re a dean at the University of Michigan! We’re sure you get excellent health insurance and retirement benefits, so is it really worth selling your good name to be a pretend “lead author” of something you probably spent a few hours red-penning over your morning coffee? Let’s get real: Scholastic really should have used its budget to create interesting and compelling content, instead of squandering it on empty endorsements, outdated methodologies, fancy graphic design and inept copy editing.

This post was brought to you by the entirely unprofitable concern known as SamizdatMath, and matho-educational syndicate which develops and self-publishes uncompromising mathematics materials for teachers in grades pre-K and above. This particular rant was brought to you by:

What is a “Skill?” The Trouble with Remainders….

Base 12: No Mo' Remainders!

Readers, do you live in fear of teaching division to your students? Do you stay awake at night laboring over unique division examples that come out evenly? Do you squirm every time a student looks up and says, “but blach doesn’t go into blah-blah-blah?” Do you drift off into la-la-land whenever a student complains, “hey, there’s a remainder here; what should I do with it?”

If this bothers you, then consider the options of using the duodecimal system, aka “base 12.” In the base 12 number system, you have many more options to give division problems that are “remainder free!”  Yes, now you can strike one less issue off your list: fewer remainders means neater division problems, no complaints about extra numbers and, most importantly, fewer decision to make! With the duodecimal system, you can divide by 1, 2, 3, 4, 6, and 12 without worrying about pesky remainders! Try that with the crummy old decimal system: divide by 3, 4, 6, 7, 8, and 9 and what do you end up with? REMAINDERS! Urgh!

Okay, the world will not be switching away from the base 10 system anytime soon, and remainders are going to be a fact of life well into our collective future. So the question is this: what should you tell your students to do with the remainders that inevitably come from dividing?

a) Do the problem over; all division problems in school come out evenly.

b) Write it as a whole number, and let someone else deal with it.

c) Leave it as a fraction, whatever that is.

d) Leave it as a decimal, so long as it comes out evenly. If not, refer to choice “a.”

e) Round up to the nearest whole number.

f) Round down to the nearest whole number.

g) All of the above.

h) None of the above.

i) Check Khan Academy.

j) It really depends; remainders on division problems are highly contextual.

Well, if you know my style of writing, you know the answer is “j,” but given how many teachers treat math as a set of “rules” to be obeyed,  it is most likely that a student will choose a, b, c, d, e and/or f. Harumph….

The simple fact is this: most division problems do not come out evenly, and why we persist in giving students a steady diet of problems that leave no remainders is beyond my comprehension. The presence of remainders should not be seen as an “oddity” when dividing; rather, we should teach it as one of the essential properties of how division works: most numbers do not go into other numbers evenly, or even once (the “bigger into smaller” issue, which I’ll cover in another rant…), and yet we persist in giving students a steady diet of division situations which work out evenly. Therefore, if we give word problems where remainders are the exception, rather than the rule, our students are not going to have strategies for dealing with remainders.

Consider the five problems shown below, all of which have remainders, all of which require different interpretations.

In the first problem, the remainder gets discarded, while in the second problem, the remainder should be written as a decimal. The third problem is best left as a fraction, the fourth problem needs to be rounded up and the fourth problem doesn’t even need division at all: just multiply 7 boxes times 6 donuts per box and you end up with 42, which is larger than 39. Do I have to do everything for you?

Teachers of mathematics, we have to wise up! Give your students lots of word problems where the divisor doesn’t gozinta the dividend evenly, and have them interpret the meaning of the remainder. It’s either that, or push for decimal reform and invest in base 12 calculators!

This post has been brought to you by the hardest division assessment you could ever give to a student who believes “I know everything there is to know about division.”

Hand your students a calculator and watch their brains sizzle! Comes complete with teaching tips, answer key and suggestions for activities that you can do in the classroom.

In my 32nd year, there’s still more to do….

I started teaching waaaay back in 19, wait for it, 84. I was a much younger man back then, and while I thought it seemed like a good way to earn a living, I had no idea the actual “craft” would engage me for more than three decades. Back then, I honestly believed that it was all about teaching a few skills and then testing to determine how much my students remembered. In that sense, I believed that teaching was like running a series of controlled experiments: teach, test, teach, test….

As I struggled through the first year, the head of school, with whom I found myself at odds with, offered me a book called “The Art of Teaching” by Gilbert Highet, which actually proved to be my undoing when I attempted to implement the ideas expressed. I had actually read another book about teaching when I was 14 years old, 36 Children by the wonderful Herbert Kohl, which got me thinking about teaching as a force for social justice. My first year was rough, but it was then during that year that I understood, I was born to teach. I also learned that the idea of “teach, test, teach” just was not the essence of the profession. There was much, much more to learn and do….

The Art of Teaching & 36 Children

Two definitive books on teaching; both were “borrowed” and never returned to their owners.

Flash forward 32 years, and here I am, back where I started: a new year, new thoughts about teaching, and new things to do. I stopped in to visit the lovely teachers who rule the 2nd grade (or, what we call the “7/8s”) and what did I find but a lovely activity based on Eric Carle’s beautiful story, Rooster’s Off To See The World. As with all of Carle’s books, the illustrations are engaging, and the story works on many levels – it is nominally about a group of animals out for adventure, who ultimately opt for the “creature comforts” of home. At the same time, it is a counting book, designed to introduce the young to numbers and patterns. The teachers had posed a problem to the students: if there are 14 animals off to see the world, how many legs would they have? This is not an easy question, because some have 2 legs while others have 4, and there are 14 numbers to keep track off, which is no easy task for a child (or even an adult.)

I looked at the book very carefully and decided for myself, well, this is a wonderful book and the idea of keeping track of legs on animals is a provocative one for young children to do. But I also thought that turning the tables on the activity, that is, giving young children the chance to ask questions of one another, would be a fun and engaging way to get them to interact with one another.

There was just one problem with this plan: there is a great deal of variety in the legibility and spelling of 2nd grade children, as well as their motor skills in writing out questions. I wanted them to create problems quickly, so that they could focus on the mathematics, rather than letter formation, sentence structure, grammar and punctuation, to name a few elements of literacy. I also didn’t want to get into trouble with the publishers of Mr. Carle’s book due to copyright infringement, which meant staying away from his imagery and characters.

Instead of rooster, cat, frogs and turtles, I decided to simplify the activity by using only 3 animals. At the same time, I wanted to vary the number of legs on the animals, that way I could have more combinations: so I used an ostrich (2 legs), wombat (4 legs) and ants (6 legs.) I also think that ostriches, wombats and ants are interesting animals, don’t you?

With those decisions made, I designed three different stamps that students would cut out to make their questions: instead of writing out long sentences with stories, I envisioned them cutting and pasting combinations of the animals, with the simple question “How many legs?” printed underneath.screenshot-2016-09-26-11-26-27


Well, this seemed like a promising start, but why stop at just addition? Since subtraction is also a good topic, why not create a simple problem that involves comparing the number of legs?


and while we’re at it, why not add something even more interesting and open ended?



Oh, this is muy muy fun, and if you don’t agree, well, you just don’t know what the definition of fun happens to be….

To add finishing touches to this activity, I thought about what could be done to get kids to think more carefully about how they create their problem, as well as offering a means to initiate discussion of their solutions. Which is why I created a separate sheet where they could make an answer key for the question they asked, as well as offer a “clue” about how to approach solving the problem:


Isn’t this beautiful? Well, that’s not all, because I added one more innovation which I think I may use on every single activity I make in the future:


Do you get what I’m attempting to do here? Instead of putting the name of the students at the top of the paper, which is what you do when you start something very monotonous (like take a test or apply for a learner’s permit at the DMV), I thought it would be much more important that a student “sign off” on their work after it has been created. Much like no artist every signs a work before creating a sculpture, painting or dance piece, a student should not sign off on a piece of mathematical thinking until after it has been completed. This allows the student to feel a sense of process and completion to what they have done. I feel very inspired by this tiny little change, and I hope you’ll use it as well.

The scariest thing I can imagine about being in my profession is doing the same thing year after year. Working with a staff of vibrant educators means that I always have the opportunity to do more and more, as well as refine what I’ve already done, AND share it with the rest of you. At 32 years in, I’m still feeling young…


This post has been brought to you by…..




How Long Before I Know I Suck At It?

Robert has a lot of stories about what goes on in school each day, and often he recalls these stories whenever he is in the middle of some educational rant, which usually occurs when he reads an article on what he calls “the interweb.”

Robert's superhero psychologist, Carol Dweck

Robert’s superhero psychologist, Carol Dweck

Carol Dweck, author of “Mindset: How You Can Fulfill Your Potential,” has long been one of Robert’s favorites in the field of educational psychology (his shortlist of the overrated and the “just plain terrible” includes Jo Boaler, Dan Meyer and Angela Duckworth, who all started out with such promise….)

So when he spotted this article posted on the The Facebook, Robert was reminded of the necessity of talking to children about how they should view themselves in learners. Now, Robert works with kids as young as 4, all the way up to 14, so in this decade long span, there are lots of ways to communicate how one gains proficiency in mathematics, but it must be consistent and constant.

Here’s his story:

“I was working with a fourth grade class one morning, when a young man sat down next to me to work on a set of geometric puzzles I had created. As he worked, the child got more and more frustrated, and eventually muttered aloud, “man, I really suck at this.” I looked over at what he was doing and said, “yeah, a lot of kids find this tricky at first. It usually takes them a long time to finish the first few, but then once they get familiar with the pieces, it gets easier.”

Of course, the kid fell asleep during my soliloquy, so much of what I said was ignored. He went back to work, and after a few minutes once again stated, “I really suck at this.”

Remembering my grad school professor’s admonition that I talk like kids talk, I turned to him and asked, “Mergatroid, how long have you been working on this puzzle, anyway.”

“Oh, it must be like an hour…”

(It was actually more like 5 minutes; maybe he needs to try out this activity to sharpen his skills at time perception.)

I corrected his time assessment, and said the following:

“You know, you can’t know if you suck at this yet; it’s only been 5 minutes….”

“Well, how long will it take me to know?” he replied.

I thought about his question very carefully. On the one hand, I wanted to be realistic that some things in mathematics take time to understand and master, yet I wanted to encourage him to persevere to completion of the task.”

And with that, I said this:

“Oh, I would say about 20 years….”

“20 years?”

“Yeah, I’d say 20 years would be a fair amount of time to spend on something before you could say you sucked at it. You really don’t suck at these puzzles yet.”

“So you’re saying I should spend 20 years working on this puzzle?”

“If that’s what it takes; but my guess is that it won’t take anywhere near that long…”

And with a shake of his head, my friend went back to working on the puzzle, which he later solved in the afternoon.

This (thankfully brief) story summarizes a lot of what Carol Dweck has been trying to advocate in her work, albeit with a twist. According to Dweck (who is not the first person to advocate for the “growth mindset,” by the way), the most important word to use when describing the challenges facing a child is the word “yet.” When we use this common and simple word, we are expressing our confidence that a child will persevere when facing a challenge which appears to be overwhelming.

The pivotal moment in Robert’s understanding of this word was when he was evaluating a young man whom he observed banging his head during a class he was visiting in North Carolina. When he sat alone with the child later in the day, he asked why he felt so challenged by math.

“Teacher says I don’t know my multiplication tables,” he explained.

“Oh,” I replied, “well, that’s a very common problem, even for adults. Tell me, what is 5 x 4?”

The young man responded, “5 x 4 is 20.”

“Oh, so you do know that one. How about 6 x 6?”

“6 x 6 is 36.”

“Good; how about 9 x 5?”

“9 x 5 is 45…”

This went on for about ten minutes; what it turned out was that this boy knew almost all of his multiplication facts, with the exception of the “difficult” ones (8 x 6, 7 x 8, 6 x 7, etc.) Every time he came upon one of these facts, he was reminded of what his teacher said and got angry at himself.

“You know, Will, the problem is not that you don’t know the multiplication facts. There are only about 4 or 5 out of the hundred facts that you are still stuck on. You don’t know all the multiplication facts yet.

With that, Robert could see his man’s face change a bit. He continued:

“Knowing 95 out of 100 facts means you know 95% of of the multiplication facts; in my book, that’s pretty good. Sure, you should learn the other 5%, but that wouldn’t be that hard, would it?”

And with that, young Will actually started to smile.

This little word has been Robert’s favorite word to describe the challenge of learning mathematics, whether it is a 4 year old struggling to count to ten or a 14 year old attempting to factor a quadratic equation.

“You can’t be bad at this yet. Give it 20 years, and if you haven’t seen yourself improve, well, then you can say you’re no good at it, okay?”

“But Robert, 20 years is a long time!”

“Well, you don’t want to give up too soon….”

This post was brought to you by the following resources Robert publishes and even makes a few pesos from now and then:


Wasting Time & Paper, Wasted Thought: Cut ‘n Paste Optimized

Robert has a new Pinterest board called Fraction Teaching Mistakes where be trolls through the wide world of what passes for “good” mathematics materials and comments on the inherent flaws in one activity or another. Some he objects to because they hide the underlying beauty and logic of mathematics through “magical thinking” (for example, “butterfly methods” for comparing fractions), while at other times he finds very rigid representations (“will we ever see the end of fractions represented as pies?”  he often laments…), not to mention information that is just plain wrong (2/5 x 1/3 = 11/15?)

Materials like this focus on “peripheral” activities like coloring in shapes. Avoid at all costs!

One of the things that really irks Robert are math activities that focus too much attention on peripheral activities, like coloring, cutting and pasting. These projects look very pretty when completed, but unless the teacher’s specific goal is to create a work of art, they are pretty much a waste of time.

At the same time, it could be useful to take a break from using pencils and screens to do math, and cutting and pasting are good for motor skill development, so why not let the kids have a change of pace? How can we design a cut ‘n paste activity that makes the most of a student’s limited time in math class, without unduly devoting the majority of time on scissors and glue? How can we maximize the amount of thinking that will take place?

One thing that has to be considered is on designing the “cut outs” so that it can be cut out efficiently and with a minimum of wasted paper (which is why Robert objects to the use of most “cutesy” clip art that routinely gets inserted into many materials.) Check out the “cut outs” used in a 3rd grade activity below:

cut n paste bad example

There are three reasons to object to this: the first is that it is difficult for young children to cut out, what with the individual pieces and rounded corners. The second is that there is a lot of white space between the different “cut outs,” which mean that it is a waste of paper. Third, since there are more symbols than actual problems, the students will be cutting out materials that are unnecessary. While the activity may be useful, this is seriously bad design. After making all the cuts (there are 13 separate pieces, at 4 cuts per piece, which is 52 different cuts, not to mention the time rounding out the corners) how much time do you think will be left to “do math?”

Robert approached the “cut ‘n paste” activity and redefined it as a design challenge, seeking to have the most “work” with a minimum of cutting. Here’s what he came up with:

cut n paste good example

What you’ll notice is that there are no rounded corners to trim, and that almost every piece is adjacent to another, so that one cut actually trims 2 separate pieces. The 24 pieces can be separated from the main sheet with two easy straight cuts, and then laid on top of one another two at a time to minimize cutting. The fifth graders who did this activity typically were ready to place their pieces in fewer than a dozen “cuts,” which look about 3 – 5 minutes. In addition, there was a minimum of paper waste, as the activity only left behind two small squares of paper and 2 thin strips.

Since Robert is a calculating guy, he figured out that there was less than 5% wasted paper, and 90% less cutting than other activities of this type. With less time on cutting, the students had much more time to think about much more important things, like “if 1/7 is .142857 on the calculator, and it’s rounded off to .142, why isn’t there one on the sheet?”

This post has been brought to you by…..

How to do a lot of damage to a kid’s understanding of math in one simple chart….

Robert has been accused of being a serious badass when it comes to mathematics, most likely because he is very adamant about “getting things right.” According to Robert, “there are no shortcuts to understanding,” when it comes to understanding math, but if you look at the materials that are being posted on the web these days, you would believe that manipulating numbers is nothing more than memorizing a dozen or so “rules.” So when this poster showed up on Pinterest (luckily the link to the miscreant was not included), Robert lit’rally blew a gasket:

Would the teacher responsible for this please step forward?

Where does one begin to explain all the problems with this?

The beginning part of this is not all bad: true, multiplying by 2 is also the same as doubling, and yes, you could double a double to multiply by 4. But really, do you think there are a lot of 8 and 9 year olds who can double a double a double?  You can almost see the smoke coming out of little Hudson’s ears as he attempts to double 8 three consecutive times: 8 + 8 = 16, 16 + 16 = 32, 32 + 32…. wait, where was I?

Things only get worse as you get further down the chart: yes, multiplying by 0 always equals 0, but does a child really need to memorize this fact? If the student understands the meaning of multiplication, then reciting “times zero = zero, zilch, nada….” and “times 1 = the other factor” is just nonsense. These are essential features of our number system that require understanding, not memorization: times 0 is the “zero property of multiplication,” and times 1 is the “multiplicative identity.” Yes, the word “multiplicative” is a mouthful for a young child, but this chart totally ignores the totally interesting properties of 0 and 1.

But the real howlers are multiplying by 10 and 100. The “adding zeroes” shortcut is incredibly wrong and will only lead to misconceptions the following year when the student learns about multiplying decimals, when he will end up writing down the following:

...and this is what your fourth grader is going to do....

Follow the chart and this is what you end up with…

Make no mistake, this error will not go away in 5th, 6th or 7th grade. In fact, the idea that you multiply by powers of 10 (whether that be 10 or 100 or 1,000 or 10,000 and onward….) by “adding zeroes” is a hard one to shake at any age.


What should we do instead? Show students that multiplying by 10, because we are in a base ten system, “pushes” all the digits over one place to the left, and that zeroes “rush in” to fill those places that are left empty….

The "right" way to multiply by 10s and above...

The “right” way to multiply by 10s and above…

The beauty of teaching multiplication by powers of ten this way is that it will always work! It will work with whole numbers, negative numbers, decimals, irrationals, rationals, you name it, it will work!

This post has been brought to you by this guide to teaching place value, from which it has been excerpted:

C'mon, you know you want it.....

C’mon, you know you want it….



Enough with fractions, already….

Robert is an occasional reader of our hometown paper, The New York Times, and usually rolls his eyes whenever one of the cub reporters attempts to make sense of mathematics education. Every once in a while, however, the editors manage to slip up and allow someone with an ounce of common sense to write about his chosen field of expertise.

Such was the case when a reporter covered Andrew Hacker and his very convincing case for eliminating the traditional “advanced math” curriculum. We all know this as the algebra-geometry-trigonometry-advanced algebra, yadda, yadda, yadda forced march that college and capital accumulation bound high schoolers must march through. This sequence allegedly prepares the few students who actually understand this stuff for brilliant careers in art history, restaurant management and human resource development. It’s not that Hacker dislikes mathematics or wants to dumb it down; rather, he suggests that maybe a more thoughtful approach focusing on “real life” uses of mathematics would actually achieve the goals we have set out: prepare our students to participate in our quasi-capitalistic economic life and pseudo-democratic political system.

While we’re at it, Robert wishes Hacker would also take a more courageous stand, and push back against the teaching of fractions in the elementary grades. Talk about a waste of time: while fractions were a useful thing to know if you were a working class Sumerian over 5 millennia ago, today they’re just that like that unwelcome uncle who pops up at the Thanksgiving dinner table each year: nobody knows why he’s there, and everybody would digest much easier if he just stayed in his cardboard box.

Screenshot 2016-03-14 09.35.35As Robert tells it, fractions had a good run, and with a 5,000+ year history, they’ve outlived every fad imaginable, including paisley togas and virgin sacrifices. Fractions began their long run with the Egyptians, who utilized them to divide up plots of land and levy taxes. The ancient Sumerians loved fractions so much that they invented the 24 hour day, the 60 minute hour and the 360 degree circle just so they could divide them up into equal pieces really easily: a 24 hour day can be divided into halves, thirds, quarters, sixths, 8ths, 12ths and 24ths (don’t get me started on how easy it is to divide 60 and 360….) You just can’t do that with 10 or 100.

But Robert maintains, fractions are pretty much dead so far as common usage goes, and you can blame that on the French. Yes, those Jerry Lewis and croissant beurre loving eggheads are to blame for the downfall of fractions and the rise of its bitter opponent, the easy and convenient (and mostly sanitary) decimal notation. Quelle barbe! 

Typical French citizen holding 300 ml glass of wine with 1 meter long baguette and smoking 100 mm cigarette. He'll probably live to be 100 years old....

Typical French citizen holding 300 ml glass of wine with 1 meter long baguette and smoking 100 mm cigarette. He’ll probably live to be 100 years old….

Whatever your feelings for the French, which can be determined by what you call fried potatoes served with ketchup, you’ll have to admit they were on to something by inventing and then adopting the metric system: it’s soooo easy to use! No one who has ever worked with kilograms, meters or liters (as well as newtons, joules and candela) has ever had to struggle finding a common denominator, convert to a mixed number or inverting and multiplying. Is it any wonder that 99.9% of all the countries in the world use decimal units of measurement?

But here in the United States, we love our fractions, which means that it is the only place on earth (well, toss in Liberia and Myanmar) where fractions have to be taken seriously. Open a cookbook and what do you find? Fractions of a pound, fractions of a cup, fractions, fractions, fractions! Robert believes cooking is a pretty pleasurable experience, up there with consensual sex, open-water swimming and playing the concertina, but when you mix in fractions, well, you’re just asking for trouble. Robert wagers that there is a significant fraction of the American population which hates to cook because they’re scared of fumbling with quarter cups and half-pounds.

Sorry, kids, no cupcakes today! Daddy doesn't like baking with fractions...

Sorry, daughter, no cupcakes for your birthday: daddy doesn’t like baking with fractions…

Open a cookbook anywhere else in the world, and there will be nary a fraction in sight: everything will be measured in grams, kilograms and liters, which makes life quite a bit easier. Don’t need an entire kilogram? Just put a decimal point on it, baby! Need to increase a recipe by ten times? Push those digits one place to the left and move on! You just can’t do any of that with half-tablespoons of vanilla…..

And this just has to do with cooking; the prevalence of fractions in American life, from our use of 8 1/2 x 11″ sheets of paper for correspondences to road signs which tell us our exit is 3/4 of a mile away is just so passé. I agree: I know decimals will take some getting used to when it comes to our everyday life, but can’t we give it chance?

My best seller!

Truthfully, Robert loves teaching fractions, and even makes a pretty good living off of them, seeing as how 4 of  the top 5 bestsellers at his online store are about… fractions! Even I think they have some important uses, especially when it comes to algebraic notation, and they can be rather fun when done in a playful and non-threatening way.

I really don't think this is going to fix the problem...

I really don’t think this is going to fix the problem…

However, in an era of high-stakes testing and curriculum standardization, maybe it’s time we reconsider the teaching of fractions in elementary school. Fractions prevent our students from solidifying more important concepts and mastering developing skills. They are confusing and have limited uses, yet we persist in teaching them to children who are just not equipped to understand them. Can we agree to delay them until 5th, 6th or 7th grade, when kids are more able to comprehend them, and can be covered in 1/4 the time?

I would wager that 93/95 of the American population would agree with me.

Geometry: It’s More Than Basetimesheightdividedbytwo….

Robert has been in the teaching game for a long time. A looooong time. Robert has lived through every math fad that has come along, from the “back to basics” movement right through dozens of different math programs including “Chicago Math,” “TERC,’ “Real Math,” “Mathematics in Context,” and numerous others. Let’s put it this way: when he first started teaching, he regularly called Steve Jobs’ secretary for tips on how to install a video card into the Apple IIe….. If you don’t know what the words “secretary,” “video card” and “Apple IIe” mean, you’ll know that was a long time ago….

Believe it or not, Robert keeps some of his old textbooks he used in his teaching library, and every once in a while he pulls one down for either inspiration or, more likely, to roll his eyes and mutter under his breath, “what was I thinking when I taught this?” Here’s one page that especially embarrasses him from a textbook he used in…. wait for it…. 1985!

These kinds of problems make Robert go "arrrrghhh!"

These kinds of problems make Robert go “arrrrghhh!” and not like a silly pirate….

Robert, older and wiser, looks at this exercise and knows that this is junk, junk, junk.  “Why are there pictures of triangles?” he mutters under his breath. “Don’t the writers know that the students don’t need the illustrations? They’ll just multiply the two numbers together and divide by two to get the answer.”

This is what irks Robert about how math curriculum is designed: the assumption that students are too stupid to actually think through a few steps of their own to get to a solution. So instead of having them figure out what information is important and how it should be used, they just follow a “rule” over and over and over and over again. Of course, this was back in 1985, so surely things are much better now.

Some improvement, but still not there yet....

Some improvement, but still not there yet….

Well, maybe a little better. Let’s have a look at this example, which appeared in textbook from 1990. Okay, it’s a bit better: the student actually gets to do something besides “plug and chug” a formula four times in a row, and the student does have to think about whether it should be “basetimesheight” or “basetimesheightdividedbytwo.” The student even gets to make some measurements using a centimeter ruler and round the measurements to the nearest tenth. Hey, look ma, mixed practice AND measurement in one activity!

But do you see why this exercise is a fail? Look closely: what are all those dashed lines doing there? Oh, those are the “height lines,” because we all know that asking students to both measure the parts of a geometric figure and apply a simple formula is really pushing them too hard. Let’s just make it easy on them by showing them what to measure!  Damn, Daniel, that’s sad!

Let’s jump ahead 25 years and see how things have changed. Robert enters the terms “practice” and “area of a triangle” into his browser and copies one of the first worksheets to pop up. To protect the guilty, he has eliminated the author’s name (assuming it was an actual person and not a computer program that generated this atrocity.)

It's 2016, and our students are still doing junk like this?

It’s 2016, and our students are still doing junk like this?

25 years later! Think about all the changes that has happened, including 6 presidential elections, several wars, the demise of Wilson Philips and the rise of Ariana Grande, and we’re still giving students the exact same dumbed-down tasks? If anything, this one is even more frivolous, because the measurements don’t include decimals, AND the units for the solutions are written out for the student already. Good grief, thinks Robert, what is the point of it all? Basically, these 6 problems are about as relevant to understanding mathematics as using “Grand Theft Auto” would be in a defensive driving course.

This is what Robert does when you use "dumb" worksheets in your class.....

This is what Robert does when you use “dumb” worksheets in your class…..

I fix Robert a cup of chamomile tea, pass him his favorite stress toy and wait.

…and wait…

…and wait…

When he’s sufficiently lucid, I ask Robert to tell me what he does when he designs activities involving area of polygons for his students.

“Well, the first thing is that while the formula for finding the area of shapes like triangles and parallelograms involves base and height, the fact is that any part of these shapes can be the base; the height then has to be drawn in or located. These dumb worksheets do all the work for the student: shouldn’t  the students learn for themselves how to identify these parts?”

If you said the base of this triangle was on the bottom, you would be wrong!

If you said the base of this triangle was on the bottom, you would be wrong!

That sounds fair: there have been so many times when I’ve looked at problem that my teacher gave me and wondered, “what would happen if I rotated this triangle? Would a different side become the base? And what is the difference between a ‘base’ and a ‘side,’ anyway?”

Robert doesn’t stop there. “What’s going to happen if the student ever has to find the area of a triangle in real life? She’ll be totally lost, because no one told her which side is the base and which part is the height. Then you have kids making very basic mistakes, like believing that the height is just one of the sides, which can be true when the triangle is a right triangle and you use one of the legs (the non-hypotenuse side) as the base. But what if you can’t measure those sides, for some reason? You’re completely stuck, because the problem doesn’t look exactly like the one in the textbook!”

All of which is why Robert is more likely to give the following problem to his students:


Identify the base and height of this triangle, measure them to the nearest tenth of a centimeter, and then calculate the are. Do the problem using three different sets of measurements.

Identify the base and height of this triangle, measure to the nearest tenth of a centimeter, and then calculate the area. Do the problem using three different sets of measurements.

“I’ll admit, this is a tricky problem,” Robert explains, “because it doesn’t spoon feed your students all the information needed to solve it. But isn’t that the point? Shouldn’t we get students beyond the lame ‘plug & chug’ arithmetic and have them really think about mathematics?”

And with that, Robert unwraps a new stress toy and invokes a meme….

Screenshot 2016-02-24 11.19.05

Readers who took the time to read and understand this post would most likely like to support the ongoing team of therapist who keep Robert under control by purchasing some of these materials to use in their classroom:

Screenshot 2016-02-24 10.06.24Screenshot 2016-02-24 10.08.00

Screenshot 2016-02-24 10.09.16  Screenshot 2016-02-24 10.10.22

I Scoot, You Scoot, I Suggest You Stop “Scooting”


There's a lot of "scoot" games on TpT. You shouldn't use any of them.

There’s almost 18,0000 versions of “scoot” games on TpT. Robert says you shouldn’t use any of them.

Robert has been selling materials on TeachersPayTeachers for the past few years (he won’t call them “products,” because that’s debasing his “process,” whatever that means….), and one thing has always mystified him:

What’s the deal with “Scoot?”

To those of you who have been living in a cave alongside Donald Trump, the idea of “scoot” is to number a bunch of “task cards,” put one on each student’s desk, and then have them work on the problem for a few minutes, bang a pot, or use some other signal, and send kids on to the next problem. Teachers claim it’s great because it gets the kids to practice and they can move around the room, yadda yadda yadda. 

Screenshot 2016-01-22 17.00.39

According to Robert, who has only been working in classrooms since like Neolithic times, this is a seriously bad practice, especially with mathematics.

Here be his three reasons:

Scoot sends the wrong messages about mathematics: If you’re wondering why your students can’t perseverate (yes, that’s a real word) with doing a multi-step math problem, it’s because they’ve been playing too much Scoot. Scoot communicates to children that they have to do math fast, like really fast, and then move on to the next problem. This is not what mathematics is all about. Most people who “know” mathematics understand it is an intense discipline which requires careful thought and attention to details. Scoot reinforces the idea that “good” math is “fast” math. Uh huh….

Scoot makes kids anxious: See those kids who look like they’re having fun? Robert tells me that there are a good number who dread playing this game (contrary to their willingness to “go along”), because the pace is so fast that they never get to finish a problem, and those that they hurry through to finish are often wrong. Meanwhile, all around them they see a friend who has finished their card and is waiting for the pot to be banged. Robert fondly remembers being the last one to finish anything in school, and he recalls nothing is more humiliating than watching the kids next to him finish their multiplication tests before him on a very consistent basis. And you wonder why he calls his career in teaching math “a from of revenge…”

Scoot is dumb: Okay, this is easily open to misinterpretation – when Robert use words like “dumb” and “smart” when referencing math activities, he’s talking about “smart” as giving kids the right amount of time and resources to do different levels of challenges, while “dumb” is giving exactly the same amount of time to do exactly the same thing over and over again. Since the rules of scoot demand that each problem be completed in the same amount of time, the types of problems you can give are pretty limited. That’s “dumb.”

Okay, big mouth, what’s your alternative to “Scoot?”

Robert claims he’s never, every used a “scoot” type game in a classroom, and you know what, his students get just as much practice as yours. Nyeh nyeh nyeh nyeh nyeh. Instead, Robert has his kids work on “Fishbowl Problems.” From what I understand, a “fishbowl” is where you create all different types of math problems related to a subject, making some easy and some hard, mix them up in a “fishbowl” (or a hat, or a large jar, or what have you….) and then circulating around the room letting kids take a problem out of the jar. That actually sounds kind of cool – why didn’t my teachers do that when I was growing up?

Here’s the great part: the kids don’t know what problem the other kids are working on, so if Rahim needs 8 minutes to finish a medium challenge problem, he doesn’t get anxious, because he doesn’t know what type of problem Schwarmala or Dobie or Cookiehead is working on. Moreover, he may finish that problem and then move on to a second problem which is pretty easy, knock it out in 3 minutes and then flex his mojo on a third problem. The point here is this: “fishbowl” is “smart” because there are different kinds of problems to work on and nobody get’s anxious, because there isn’t all this time pressure from the bang of a gong. A kid might select a very challenging problem and feel good that she completed that single problem in 20 minutes, while another kid may do 4 different easier problems during the same amount of time.

This all sounds kind of reasonable to me, but the question is, what should a teacher do with the dozens of “scoot” materials he/she has already purchased? Robert told me that if you add some easier and harder problems, they could easily be turned into “fishbowl” exercises.

So listen to Robert’s admonition and please, PLEASE! Stop “scooting” and start “fishbowling.”


People who liked this post also purchased this and found it “highly effective” in their classrooms.