It’s funny that both Dan and Mr. K posted about giving that quizzical look to students — the “are you absolutely sure you’re right?… absolutely absolutely sure you’re right?” face. Or, to put it in the game show analogy, “is that your FINAL answer?”

Like Dan and Mr. K, I do this a lot. Both when kids are wrong and when they are right. And just today, after I had students give me answers to a worksheet, I stood at the board. Rubbed my fingers on my chin, stroking my imaginary beard. Gave that quizzical look. And then snapped back and said: “there’s something wrong here.”

They searched and searched, and someone said they thought they found something wrong — but it wasn’t actually wrong. And in the end, after a good 45 to 90 seconds (who knows? time gets so nonlinear in the classroom), I turned them them and said: “Okay, so you got me. You got everything right.”

I did it on purpose.

This all reminds me of my calculus teacher in high school He was a great teacher, and he prefaced the course by saying he would make mistakes on purpose to see if we’re paying attention. And each time he made a “mistake,” hands shot in the air. He would pass it off like something he did on purpose. Looking back, I think a good number of times, he just had made some silly error and was covering. (Sneaky genuis!) But I can say that every so often, once in a blue moon, he would make mistakes that no math teacher would make. (Like saying .) These mistakes became warnings of what not to do.

Ah, I miss that class.