Joe Schwartz hosts a pie-eating contest:

The game consists of two circles (the pies) and a set of Angle Race cards. Partners take turns drawing a card and then using a protractor to measure off the right sized piece. Keep going until you’ve eaten your entire pie. Whoever finishes the pie first is the winner!

Joe improvises his lesson plan in two very interesting ways and he explains his thinking. That’s great blogging.

Matthew Jones gives us a nice picture of modeling in the elementary grades when he asks his students to help him put a new roof on the school gym:

Will any of them have to do this in the “real-world?” Who knows? Maybe, maybe not. But the pictures and slides set into motion a new enthusiasm about solving it because it was their school, it was their gym. It was something they know like the back of their hand. Maybe next time they’ll look up at the ceiling and remember how they figured out the area.

Kaleb Allinson and Sarah Hagan offer different but useful approaches to probability.

Here’s Sarah:

My students instantly wanted to play again. I had anticipated this, hence the double-sided bingo cards. Based on our first round of bingo, my students set out to create a better bingo card. One of my students decided to calculate the probability like I had. She accidentally left the BB combination off of her card. She was not happy about this!

And Kaleb:

I will have students make their own boards using geometric shapes that will convince someone to think they can win but that odds are still in the game owners favor. As an extension students can include winning different amounts of money depending on where you land so a player is more enticed to play.

David Cox:

I’m noticing that more kids are gaining confidence in looking for patterns, forming hypotheses and then seeing if they can make the hypothesis fail. The phrase that seems to be gaining ground when it comes to hypothesis testing is “wreck it” — as in, “Oh, you think you have a rule? See if you can wreck it.”

There are two things I love about this:

1. The phrase “see if you can wreck it,” and the toddler-knocking-down-a-tower-of-blocks spirit of destruction it conveys.
2. The fact that you are supposed to wreck your own conjecture. Your conjecture isn’t something you’re supposed to protect from your peers and your teacher as though it were an extension of your ego. It’s supposed to get wrecked. That’s okay! In fact, you’re supposed to wreck it.

BTW. When David Cox finds a free moment to blog, he makes it count. Now he’s linked up this spherical Voronoi diagram that shows every airport in the world and the regions of points that are closer to them than every other airport. “Instead of having to teach things like perpendicular bisectors and systems of equations,” he says, “I just wish we could do things like this.”

Of course you need perpendicular bisectors to make a Voronoi diagram, so David’s in luck.

Mitzi Hasegawa links up a clever game called Entrapment that helps student understand these reflections, translations, and rotations that (I’m told) now constitute the entirety of K-12 mathematics:

One table debated the transformation highlighted in today’s picture. Is the figure on the grid a reflection of the figure or a rotation?

Federico Chialvo asks his students “How safe is a Tesla?”

Jonathan Claydon poses the deceptively simple challenge to spin a measuring tape handle at exactly one mile per hour:

Most students experience miles per hour in a car. The challenge would imply “I should spin pretty slow.” Yet, the handle isn’t very long. And there’s the curiosity. What does 1 mph look like at this small scale? So they spun.

Mary Bourassa repurposes a classic party game for the sake of learning features of quadratic equations:

They would ask “Is my h value positive?” but then either interpret the answer incorrectly or not be sure whether the person they had asked truly understood what a positive h value meant. They all figured out their equations and had fun doing so. And they want to play again next week when the whole class is there. I’ll be happy to oblige.

Cathy Yenca gives Graphing Stories a go and the going gets tough (and interesting) when she runs into Christopher Danielson’s step-function:

The last video we tried today was Ponies in Frame. I heard the most awesome muttering as soon as the video began. “Oh! I get it. This one’s discrete.” [..] It wasn’t all lollipops and rainbows. A comment laced with negativity that resonated with Lauren and me was an outburst that “graphing used to be so easy, and this just made it hard.” How would you take a comment like that? What does that comment say about the student’s true level of understanding?

Jonathan Newman has his students analyze parametric motion by creating stop-motion videos.

Nicora Placa reminds us that the one of the best ways to assess a student’s understanding of direct proportions is to give her an indirect proportion and see if she treats it directly.

At a workshop last week, the following task caused a bit of confusion. “If a small gear has 8 teeth and the big gear has 12 teeth and the small gear turns 96 times, how many times will the big gear turn?” Several participants were convinced it was 144.

Megan Schmidt uses one of the Visual Pattern tasks and surprises us (me, at least) with all the different interesting equivalent ways there are to express the pattern algebraically:

They came up with the following pre-simplified expressions for the nth step:

2n(n+1) + 3
1 + (n² +n²) + (n+1) + (n+1)
2[n(n+1)] + 3
2n(n+1) + 3
3 + [(n+1)n] + [(n+1)n]
3+2(n+1) + 2[(n+1)(n-1)]
2n² + 2n + 3

For each of these, I had the student put the expression on the board. I then had different students explain the thinking of the student who came up with the expression and relate it to the pictured pattern. I saw a real improvement here from when I had them do this activity the first time last week. I had many more students volunteer to explain the thinking of their cohorts and much less hesitation to work out what the terms in the expressions represented.

Nathaniel Highstein engineers a counterintuitive moment about graphing, one that subverts his students’ expectations and creates intellectual need for new knowledge:

I love this problem because the answer becomes totally clear when you make a time vs. elevation graph — and the answer violates nearly everyone’s expectations and leads to a surprise! Many students got stuck in their initial guess, and even when we went over together what the intersection of the two lines implied, they tried desperately to draw a version of the graph where the two lines didn’t intersect. When they figured out that even skydiving down wouldn’t work, some resorted to teleportation.

Option 1. Explain how to use place value.
Option 2. Explain how to use place value while first asserting its usefulness to humanity.
Option 3. Explain how to use place value while first putting students in a position to experience life without any kind of place value.

Anna Weltman took option three:

Three fingers is Na Na Na. But four fingers — now, that’s a lot of fingers. Na Na Na Na is quite a mouthful and it’s getting hard to tell the numbers apart. Here is where the cavemen bring in a new word. Na Na Na Na is Ba.

We continue counting. Ba Na, Ba Na Na (giggles), Ba Na Na Na — now what? The kids think until — Ba Ba, of course!

I remember Hung-Hsi Wu’s frustration with incomplete pattern problems. Paraphrasing him: “You can’t find the next term in the sequence ‘4, 10, 16, … ,’ because it could be anything.” He’s right, of course, but you can find a first term and Chris Hunter turns that fact into an icebreaker and a robust exercise in justification. He asks students to “Extend the pattern ‘Ann, Brad, Carol, … ,’ in as many ways as you can.”

Not mathy enough for you? Remember, not all teachers will have a positive attitude towards mathematics. This is a safe icebreaker. You can always follow it up with the mathier “Extend the pattern 5, 10, 15, … , in as many ways as you can.”

The first week of Exploring the Math Twitter Blogosphere asked teachers for their favorite tasks. Lots of people mentioned Four Fours. Megan Schmidt offers us an interesting cousin to that task and a useful description of what makes it effective for students.

The students also developed some interesting strategies, like grouping pairs that totaled 16 and 25. By the end of the 30 minutes, every single student had arrived at the correct solution. I’m not sure if it was the physical manipulative or the puzzle-like feel of the task, but I was so proud of this group of kids.

My guess: it’s the puzzle-like feel. (Extra credit: What makes a math task feel puzzling?)