Which One Doesn’t Belong?



Let me introduce myself. I’m Christopher Danielson, author of Which One Doesn’t Belong? I write, I teach math, I parent. I write about the math teaching part of parenting. By day I work at Desmos, designing curriculum and supporting classroom teachers using technology. (Big shout out to Desmos for many things, not least of these the zoomable heart for Which One Doesn’t Belong?)

In case you’re new to Which One Doesn’t Belong? I’ll tell you the important bit up front. Depending on how you look at it, each one doesn’t belong, but for a different reason.

All of us playing Which One Doesn’t Belong? in classrooms and homes owe a debt to Sesame Street. (In fact, there was even a Sesame Street book by this same title!) But that version always had a single right answer. You got the answer right, and moved on.

In this modern version, finding a reason that one shape doesn’t belong is only the beginning. Next, you’ll want to hear why someone else chose a different shape, or a different reason that they chose the same shape you did. Which One Doesn’t Belong? is a way to start delightful conversations.

The Which One Doesn’t Belong? student book contains a brief tutorial and a carefully crafted and curated set of Which One Doesn’t Belong? prompts. The teacher guide provides ideas for using Which One Doesn’t Belong? in your classroom, and extensive examples of the mathematically powerful ways children talk about geometry in response to these prompts.

Welcome to Which One Doesn’t Belong? I’m glad you’re here, and I hope you’ll join the conversation!