Awesome stuff 1: Curvahedra

This is Awesome Stuff Other People Have Made Week on Overthinking My Teaching. So much great stuff to share.

First up is a Kickstarter campaign from Edmund Harriss, who makes beautiful and brilliant things. His coloring book Patterns of the Universe was part of the Summer of Math. He invented a new spiral.

Anyway, Curvahedra is a system of pinwheely spirally things that attach to each other in a simple and clever way, and which then allows you to build strange and interesting 3-dimensional objects. He brought samples along to Twitter Math Camp this past summer, and they are clearly quite wonderful.

If you are able, you should throw 10 bucks or more into the pot over at Kickstarter so you can play along when they ship next spring.

Or will the MTBoS Blogbot be unable to notice a self-referential blog title?

Reporting to parents, continued

A while back, I wrote about information that Dreambox and XtraMath send to parents about their child’s progress. Now I’d like to share some more actual feedback, but with a different contrast, brought to my attention by an alert reader.

I will keep the source anonymous by request.

Consider these two year-end summaries, both for the same child. One is by the child’s regular classroom teacher, and the other is by the child’s math teacher. This is a school where children are shuffled for math instruction.


[Child] has worked hard in third grade to increase her literacy skills in becoming a life-long reader and writer. She’s a mindful reader when choosing books of personal interest and challenge level. She reads with superb confidence and stamina. As a reader and writer of nonfiction, [Child] researched an animal of interest and published a book that demonstrated expertise of the topic. She crafted nonfiction text features that reflected her individual voice. She read and analyzed poetry—then applied the tools of a poet to craft individual poems. Wow! You’re an amazing reader and writer! Way to go, [Child]!


[Child] has made progress in math this year. She should work on learning her basic subtraction and multiplication facts over the summer. I have enjoyed having her as a student! Have a wonderful summer, [Child]!

I understand that these are different teachers, and I understand that [Child] probably spent quite a few more hours with the literacy/home teacher than the math teacher. But I don’t think those are the major things at play here.

The difference in the richness of the description of [Child]’s current literacy and growth from the description of [Child]’s mathematical knowledge and growth reflects the ways we view these two subjects in American schooling.

Throughout my own children’s elementary schooling, I have seen deep and rich attention paid to their learning to read and write, and surface, fact-based attention paid to their learning math.

Literacy is about power and beauty and self-actualization. Math is about memorization and speed. These are the ways we represent these subjects to parents, teachers, and children.

Happy kindergarten surprises

I was at a table full of kindergartners playing with triangles, trapezoids, and concave hexagons. We were building and chatting. They wanted to know if I wanted to hear them sing in French. I said yes. The sweetest two minutes ensued as this table’s Frere Jacques spread to the next and then the next, and soon the whole classroom was singing and doing math.

A few minutes later I made this.

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And then I went scrambling for my notebook.

Yup. Sure enough. (a-b)^2+4(ab)=4(\frac{1}{2}ab)+c^2 is equivalent to the Pythagorean Theorem.


Adventures in fourth grade

A few months back, I got an email from a local suburban elementary school. They had been given a bit of money to “give all of our fourth graders a unique math experience,” and they were seeking advice.

My first thought was, “Send them all to New York to visit the Museum of Math!” but this was off by a couple orders of magnitude.

As the conversation continued, it became clear that they weren’t seeking advice so much as someone to make it happen. So I said yes.

I am spending three Thursday mornings, and one afternoon, with these fourth graders. Today was day 1.

The theme of the residency is scale. We are playing with small versions of big things and big versions of small things.

A few favorite moments from today:


When asked to share a big version of a small thing, one girl said “Horses”. I pressed her to state her meaning. “If you had a map with stables on it, the horses in those stables would be really small, then when you went to the stables, the actual horses would be really big.”

Ladies and gentlemen, I give you the big math idea of inverse!

I thought the horses on the map are small versions of the big real-life horses. But she was very clear that her experience was small horses on the map, then see the big ones. The small-to-big relationship isn’t just the opposite of the big-to-small one; it is its own relationship. These two relationships are inverses—each existing on its own, but with a special connection to each other.

Which One Doesn’t Belong?

I cooked up a little Which One Doesn’t Belong? set in preparation for our work.


Which One Doesn’t Belong? never disappoints. (Student/home version and Teacher Guide coming this summer from Stenhouse, by the way!)

We noticed all the things I had hoped for, and more. And then afterwards a girl came up to me to make her case that we weren’t being totally precise about our description of the upper-right image. If—as we claimed—the shape in the upper right is composed of four of the upper-left triangles, then the big triangle wasn’t exactly the same size as the one in the lower left because the triangles have outlines which are not infinitely thin.

Composing triangles

I brought in many small laser cut triangles of these seven types:

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I gave them time to play with these triangles. One student said she knew what we were going to do with them. So I asked her what that was, and she replied that we were going to see which ones could fit together to make other ones. This was not the plan, but was behavior I was eager to encourage.

She asserted that the pink and the black make the red.

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This was a detour worth five minutes, so we took it. Arguments were presented pro and con. The major pro argument was based on the close enough principle. Con arguments were of two flavors: (1) put the red underneath and you’ll see some red peeking out from underneath, and (2) the long side on the pink plus black shape is not straight, while it is on the red one.

Composing similar triangles

The main question I wanted to get to—remember that our focus is scale—was Which of the triangles in our set will do what the upper-right shape in our Which One Doesn’t Belong? set does? Which of our triangles can you make into a larger version?

Spoiler Alert!

All triangles do this. But these fourth-graders don’t know that. And because they don’t know that, they got to feel a little thrill of success when they found one that did.

And of course they produced some evidence that the relationship we’re investigating is a challenging one.

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This is what we had on the document camera at the end of one of three sessions this morning.


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Do you see? All the others use four triangles to make the bigger version, and this one can too. But this can scale up to make a bigger version that uses only two of the original!

Of course there is a part of my math-major brain that knows this about isosceles right triangles, but it’s a wonderful wonderful thing to have pop up unexpectedly in the middle of fourth-grade math play.

Overall, a delightful morning of math. We got to only a small fraction of what I’ve got chambered so we’ll pick up where we left off next week. I’m hoping I can get them to build one of these.

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Either way, I am thankful for the opportunity to play math with this group of kids. They are creative, enthusiastic, curious, and delightful. Their teachers have been very welcoming and open to the intellectual chaos I began to unleash today.


I chose a set of triangles that would have interesting variety and some discoverable properties.

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Purple: 3-4-5

Pink: Isosceles obtuse

White: Isosceles right

Red: 30-60-90

Light blue: One-eighth of a regular octagon

Black: Equilateral

Dark blue: One-fifth of a regular pentagon

I also made some yellow obtuse scalene triangles, but they are missing so they didn’t make the trip. Within these classes, these triangles are all congruent. Each class has at least one side that is one inch long.

The sequence machine

The fun we have had with a Lakeshore Learning Multiplication Machine in our house is well documented. Not once has that fun been based in the machine’s original purpose, and I am here once again to report to you on a new off-label use for these things.

You should know that Lakeshore Learning makes a machine for each of the four basic operations: addition, subtraction, multiplication, and division. You should further know that they got the structure of the subtraction and division machines wrong (more on that at end of post). So today, I’ll focus on the addition and multiplication machines.

These have the same format as each other: 9 rows of 9 buttons. Each button labeled on top with m+n or m×n  accordingly, in the mth row and nth column. The button pops up when you press it; down when you press it again, like a ball-point clicky pen. On the front of the button, visible only when popped up, is the corresponding sum or product. Lakeshore Learning views them as mechanical flashcards and nothing more.

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I convert them to Pattern Machines by covering all the numbers with colored vinyl. These are a ton of fun at home and in classrooms—great for patterning, counting, making pixel pictures, etc.

Now I am playing with a Sequence Machine. I have covered all of the tops of the buttons on a Multiplication Machine.

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Now you can generate number sequences, without being distracted by the multiplication facts. Above, you see a familiar sequence—the squares.

Things quickly get more complicated, though. If you read each of the sequences below from left to right, ask yourself What comes next?What would be the 10th or 23rd term in the sequence? and What is the general relationship between the term number and its value (i.e. What is the nth term?)

There are many more sequences to be made on these; many more questions to explore.

I’m working on a follow up question about the relationship between the sequence generated by the same button patterns on Sequence Machines built from an Addition Machine, and from properly redesigned Subtraction and Division Machines.

What is a properly designed Subtraction Machine? you ask? I’m glad you did! Such a thing would have mn or m÷n on the button in row m, column n. This is not how Lakeshore Learning makes them. They make them like this:



Parent letters

Here is an email that a friend of mine—father of a first grader in the Minneapolis Public Schools, and math-teacher-on-parental-leave—received from DreamBox, an “adaptive learning platform” for K—8 math.

Congratulations! [Child] successfully completed a group of DreamBox Learning lessons.

Are you familiar with the concept of compensation? This is a strategy that can be used to make addition problems “friendlier”. To use it, just subtract a “bit” from one number and add that same “bit” to the other to create two new numbers that are easier to add mentally.

[Child] learned this strategy by completing a series of lessons using the special DreamBox tool, Compensation BucketsTM. For example, when shown the problem 29 + 64, [Child] turned it into 30 + 63. Towards the end of this unit, [Child] was adding 3-digit numbers with sums up to 200!

On the Run: Friendly Numbers

Take turns supplying two numbers to add. The other player has to make the two numbers into a “friendlier” equivalent expression. For example if you say 38 + 27, [Child] might say 40 + 25, or 35 + 30.

Remember, your encouragement to play two or more times per week for at least 15 minutes each time will help [Child], because knowledge is built most effectively when concepts are presented regularly. You can always check [Child]’s latest academic progress on parent dashboard.

Best regards,
The Teachers at DreamBox Learning

I’ll let my friend say what he found so great here. I agree with every word.

I just wanted to share this Dreambox support email I got today as [Child] was working. This is perhaps a more impressive feature than the software itself.  Not only does it provide a very simple explanation of what skill she is learning, it provides the jargon needed to have a conversation with her: “Bits”. As a middle school math teacher that was always a roadblock for a lot of parents: the language parents didn’t use themselves when they were in math.

Compare against the report I receive on a weekly basis from XtraMath.

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You should know that DreamBox is a for-profit corporation that charges for its services, while XtraMath is a non-profit that provides its services for free while soliciting donations to continue the work.

But here’s the thing: XtraMath is not a free version of DreamBox.

Math fact practice with an emphasis on speed is not a version of conceptual development. It’s a totally different mission based on completely different understandings about what it means to learn mathematics.

DreamBox is trying to help my friend support his daughter’s mathematical development. There is an actionable message: Play with this idea that relates to something she’s been working on.

XtraMath is giving parents “the information they need to know how well their children know their math facts, and the progress they are making toward mastery.” But what are parents to do with that information? How do they support their children in moving forward?

Ultimately, this is a question about data in ed-tech. I’m not here to single out XtraMath; it’s just the case that’s in front of me each and every week. There are lots of ed-tech products out there trying to do what XtraMath is doing.

When kids do things on computers, it is easy to collect data about what they do. It’s easy to turn that into a report or a dashboard.

It is much more difficult to determine what it all means. But data without meaning isn’t useful.

For instance, what does Tabitha’s report above mean? What am I to understand about Tabitha’s mathematical knowledge based on this report? This is the major representation her school offers of her progress in third-grade mathematics. What am I to make of it? More to the point, what is a less mathematically knowledgeable parent to make of it?

But what is a school to do?

I say provide more meaning, less data.

Don’t include free as a primary criterion for adopting materials.

Create and invest in things and experiences that support all caregivers in supporting their children’s mathematical development.

Lay off the speed-based fact practice and find ways get kids talking, thinking, and doing.

And what is an ed-tech company to do?

Invest its limited resources in crafting materials consistent with research on children’s learning and on parent communication.