This is where math meets biology.

I don’t know very much about leaves, but I feel quite certain that the things I notice about these leaves probably matter to biologists. I feel comfortable talking about how the one in the lower right is made up of a bunch of little leaves, even though I don’t know for sure what word biologists use for that. Similarly, the rounded tips of the leaf in the upper left probably have a term to describe them.

It’s the same with math. Children can notice properties of mathematical objects before those properties have names. The properties are the important thing, not the vocabulary list. Which One Doesn’t Belong? is a tool for getting students to notice, describe, discuss, and even argue over properties before worrying about terminology. Try it with the leaves and let me know how it goes.