Which One Doesn't Belong?

If you haven't heard about this great discussion technique, Which One Doesn't Belong (WODB) allows students an opportunity to construct viable arguments and critique the reasoning of others (Math Practice 3). I first learned about this from Mary Bourassa's website wodb.ca. This site provides many pre-made puzzles but making your own isn't very difficult.

These puzzles work great for my warm-ups as students walk into the room. Here is an example:

Each box contains a shape (or anything you want to study) and students are asked "Which one doesn't belong?" Student find this to be an easy problem. But asking a student to explain why it doesn't belong requires a student to have a good grasp on academic vocabulary and the ability to create a viable argument.

The problem on the left shows that every box can be used as an answer as long as you have a reason for it. The first box doesn't belong because it doesn't have equal length sides. The second box doesn't belong because it is shaded in. The third box doesn't belong because it is rotated. The last box doesn't belong because it has five sides.

To the right is my first attempt at creating my own WODB problem. My students are studying systems of equations. Each box has a reason for not belonging. I was amazed at the conversations that came out of answering this simple question. This problem sparked a discussion about solutions, graphs not showing everything, and parallel lines.

I am definitely going to create and use more of these problems to start math discussions in my class. I will post more as I create them.