Actually, if you had asked me at about 7:30 this morning, I couldn’t have told you. I was tired. Crabby. Feeling overworked, overweight, over-scheduled, and under-appreciated. In need of that last hug from my boys, hoping that extra squeeze could set me on the right path for the day. Close, but not quite.

On to a meeting. I think everyone else there had the same Crab Factor (it’s a technical term) as I did. Left with a cup of hot cocoa and a desire to go hide.

OK…before I go on, I have to say that you mathophiles out there will totally get this activity and maybe even want to try this out. You mathophobes out there…well, I promise there’s good stuff by the time you get to the end.

I love to play the calculator game with kids. It’s simple to learn, but oh so rich. (For those of you wanting to use this activity, I’ve typed up instructions and variations below.)

So that was my lesson plan with fifth grade today. To let them see the Great Unfolding of the Calculator Game. Of course they’ve played it before. But they didn’t know what it’s really ABOUT. And today I was not only going to teach them, I was going to give them time to practice these feats of superhuman intelligence.

My secret number was 120. And what did they pick? 150. And what did the calculator show? 1.25.

I was going to let them play the game out. I was going to let them just guess as they had been. I was going to move on with my lesson as planned. But my mouth worked faster than my brain. I told them that if they worked at it, they could get the secret number on the second guess – spot on.

You think the kids were going to steer away from a challenge like that, or hijack my lesson for the next thirty minutes? You guessed it.

It was interesting. Two children clearly had the concept and were trying to explain that the answer was 120. They were fighting an uphill battle against the kids who still were developing their ideas of number and percent, who felt that the group should guess 125. Believe you me, I learned a LOT about their understandings and misconceptions. Conversation went something like this:

“The number has to be 120 because 1.25 is 1/4 above the number. There are 4 30’s in 120 and if you add 30 to it it’s 150.”

“It’s 125 because 25 above the number is 150.”

“If it were 125, the calculator would read 1.2 when we put 150 in because 25 is 1/5 of 125.”

…and on and on. I reminded them that they could work on showing their thinking with a mathematical representation. Somehow, only those two students could figure out a way to mathematically show their thinking. They came up and showed their work: 25%=30, 50%=60, 75%=90, 100%=120, 125%=150.

The lightbulb went on. It was unanimous. All guessed 120. And all breathed a sigh of relief to know that they did indeed get the secret number – spot on.

Yes, I loved that they got the right answer. But what I really loved? Graduating from one level of listening to another. In the space of this conversation, students did away with the I’m-looking-at-you-and-demonstrating-listening-behaviors-but-really-not-caring-very-much habits of listening. So what did they do?

They listened and spoke with the goal of understanding and being understood. They asked each other questions, and forced people to explain further when they didn’t follow their reasoning. They discovered how tough that was – on both sides.

So why did I get up today? To experience the same joy that they do in learning. To remember the pride of making a discovery. To see what magic sometimes happens when lessons don’t go according to plan.

<<how to play the calculator game>>

Take a simple calculator. Secretly tap in a number, divide it by itself and press “=.” The display will read 1. Your opponent will then guess numbers. Tap in the number and press “=.” If the number’s too big, the display will show larger than 1. Too small, and it’s less than 1. Keep guessing numbers until the calculator displays 1. That’s how you know you’ve found the secret number!

Kick-it-up 1: Make a table of guesses and displays so they can track their thinking. (Good for learning greater than/less than)

Kick-it-up 2: Let them play each other. Even primary kids love this activity!

Kick-it-up 3: Let them play each other, but make them round to the nearest hundredth.

Kick-it-up to notches unknown: Do your kids know anything about fractions? Decimals? Percents? That’s what this game is really about. Does that calculator show 0.5? Then your guess is 50% of the secret number. Kids think I am TOTALLY whacked when I tell them I can deduce their number in 2 guesses (3 on a bad day). And then I prove it. Booyah!