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.
Megan Hayes-Golding 
Wanna share your slides / whatever they are? I’d love to see what you did in more detail, and steal / borrow it if it would work with my classes. It sounds great.
Check out the update above. One thing missing from the video is the live Ms. Golding who acts like every problem is a brain-buster. I used lots of chin-scratching during class today.
You might enjoy the book Fallacies in Mathematics by E. Maxwell.
http://amzn.to/cWMkod
That looks like fun. I think I would have enjoyed that kind of lesson in math class.