Building Thinking Classrooms,  Classroom,  Math,  math strategies,  Teaching,  Thinking Tasks,  Uncategorized

Which One Doesn’t Belong? A Math Activity for Every Learner

Which One Doesn’t Belong? (WODB) is a simple activity with big benefits. Whether you’re teaching kindergarteners or high schoolers, WODB creates opportunities for every student to engage, think critically, and share their ideas. With no single “correct” answer, this activity encourages creativity and conversation, making it a go-to for classrooms everywhere.

What is WODB?

wodb.ca

At its core, WODB presents four objects—numbers, shapes, or images—and asks students to decide: Which one doesn’t belong? The twist? Every object could “not belong,” depending on the reasoning. For example, a set of numbers might include 4, 9, 12, and 16. One student might say 9 doesn’t belong because it’s odd, while another might argue 4 doesn’t belong because it’s the only single-digit number. Both answers are valid, as long as they’re backed up with reasoning.

 

  

 

Why It Works

WODB activities are perfect because they’re:

  • Low-Floor, High-Ceiling: Every student can participate. Some might notice simple differences (like color or size), while others dig into more complex properties (like factors or prime numbers).
  • Open-Ended: There’s no one right answer, which means every student’s voice matters.
  • Great for Discussion: Students naturally want to share their ideas and hear what others think, creating a lively math discussion.

The Learning Connections

WODB is about more than deciding which one doesn’t belong. It’s about building skills that matter:

  • Critical Thinking: Students analyze, compare, and justify their reasoning.
  • Mathematical Vocabulary: Conversations help students use math terms in context, deepening understanding.
  • Collaboration: WODB encourages students to listen to others’ perspectives and consider different ways of thinking.

How to Use WODB

It’s so easy to get started. Use WODB as a:

  • Warm-Up: Kick off a lesson with a quick WODB prompt to get everyone thinking.
  • Discussion Starter: Use it to spark conversation about a new concept.
  • Exit Ticket: End the day with a WODB to see how students are applying what they’ve learned.

I like to have students go to corners of the room that I have labeled with A, B, C, D which correspond to the letters on the picture shown:

Once in their corner, students discuss with each other why they chose their response.

 

Check out wodb.ca for ready-made prompts, or create your own to fit your class. From numbers and shapes to graphs and equations, the possibilities are endless!

Defending Favorites: A New Take on WODB

Recently, at the Association of Mathematics Teachers of New York State (AMTNYS) conference, I had the privilege of hearing Howie Hua deliver a fantastic keynote on Marketing Math. During his presentation, he shared a creative variation of the Which One Doesn’t Belong? (WODB) activity.

Instead of asking students to describe why one of the four options doesn’t belong, this variation invites them to choose their favorite. One student stands in the middle of the room, while each corner defends why their choice is the best. The student in the middle then decides which group presented the most convincing argument!

I often use WODB in my professional development sessions—almost every time—to break up the day and give teachers a practical strategy they can immediately use in their classrooms. I’m thrilled to have this new variation to share with teachers and can’t wait to hear how it works in their classrooms!

Check out Howie Hua’s video explanation of the activity!

Why You’ll Love It

Which One Doesn’t Belong? is more than an activity—it’s a mindset. It shows students that math isn’t just about right or wrong; it’s about exploring ideas, thinking critically, and finding connections. And the best part? Every student has a way to shine.

Have you tried WODB in your classroom? Share your favorite prompts or student insights—we’d love to hear them!

Leave a Reply

Your email address will not be published. Required fields are marked *