Today, I made a bunch of huge math mistakes in front of my classes. Intentionally.

At the board, I simplified, added, and multiplied a bunch of rational expressions. The hook was that I’d make an error in every solution. They just had to spot it. This pedagogy is a riff on the joy kids have at telling me I’ve done something wrong.

[Edit: Here’s a quick video of the technique in action and the PDF of several problems I used today.]

I incorporated ActivExpressions, because I have a set (though this activity hardly required the tech). We held a short voting period after each solution. After a quick peek at the results, I asked a volunteer to show the class my mistake.

Some implementation tips:

- No spoilsports: tell the kids to hold their enthusiasm & corrections until the end
- label every step so kids can reference exactly where you made your mistake
- talk out loud as you solve (“I need to get a common denominator before I can add these rational expressions”)
- pause about 10 seconds between steps so kids have a chance to absorb what you just did

This lesson was a blast! My kids were hanging on every word. Seriously.