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Using Which One Doesn’t Belong in Secondary Math

This is part of the 6 Core Engagement Structures Series from Juliana at CollaboratEd

Engaging middle school math and high school math students in our classrooms often feels like an uphill battle. As educators, we strive to make learning a captivating and thought-provoking journey, one that ignites curiosity and sparks a genuine interest in mathematical concepts, but when our students have struggled with math for years or have given into the false notion that they just “aren’t a math person” engagement is a real challenge.

The "Which One Doesn't Belong" strategy changes the engagement game in our classrooms - especially for older, struggling students. In this blog post, I’ll share what it is, how to use it, where to find it, and so much more.

Understanding the "Which One Doesn't Belong" Strategy

The "Which One Doesn't Belong" strategy is an approach that encourages students to think beyond the obvious and explore mathematical thinking. Although it looks basic, this strategy is actually a powerful tool for cultivating critical thinking and mathematical reasoning. If you’re unfamiliar with the strategy, you give students a set of four items, numbers, shapes, or patterns (like the one shown below), and challenge students to identify which one doesn't belong and articulate their reasoning.

By focusing on what makes each option unique and justifying their choices, students look and re-look and re-look at the image, which fosters a deeper understanding of the math content. This strategy not only invites students to consider multiple perspectives but also promotes an environment of lively discussion and collaborative exploration, laying the foundation for a more engaging and participatory math classroom.

Benefits of the Which One Doesn’t Belong Strategy for Math Engagement

1. Fostering a sense of curiosity and exploration

One of its primary advantages is its capacity to spark a sense of curiosity and exploration within students. When confronted with the task of identifying the odd one out, students are naturally drawn into a state of inquiry, eager to uncover the underlying mathematical intricacies that set each option apart. This process of investigation taps into their innate curiosity, encouraging them to ask questions, seek patterns, and actively engage with the material.

2. Encouraging collaborative discussions and peer learning

By inviting students to articulate and defend their choices, it creates a platform for peer-to-peer interaction and shared learning experiences. Through respectful debates and exchanges of ideas, students not only refine their critical thinking skills but also learn to appreciate diverse perspectives

3. Developing a deeper understanding of mathematical concepts

As students grapple with the unique characteristics of each option, they develop a deeper insight into the principles governing numbers, shapes, and patterns, fostering a level of comprehension that transcends rote memorization.

4. Promoting a growth mindset and reducing math anxiety

There are never any “wrong answers” when a student justifies their reasoning with sound mathematical reasoning. This is the key to promoting a growth mindset and reducing math anxiety because students can feel confident that their answer is correct, which reduces the anxiety so many students feel when asked to share their math answers. This shift in attitude not only enhances their overall learning experience but also lays the groundwork for continued excitement and engagement in your math class.

How to Use the "Which One Doesn't Belong" Strategy in the Classroom

While you can probably piece it together yourself, I've seen (and experienced) this strategy work wonders when facilitated in a very intentional way:

  • Display an image set to students with the prompt, "Which One Doesn't Belong?"

  • Give them 5 minutes of think/write time

  • You can ask students to write down which ONE doesn’t belong, or you could ask them to come up with a reason why EACH one doesn’t belong

    • Optional: Label your images A, B, C, D to help students communicate effectively - this really helps ELL students access this activity!

  • Ask students, “who wants to tell us why one of these doesn’t belong?”

  • Scribe the student reasoning on the board

  • Ask, “does anyone have another reason why that same one doesn’t belong?” and scribe any reasoning on the board. Asking this question instead of just moving on to the next image will really help students see that there are many correct answers!

  • Be sure to celebrate the reasoning of students! Especially if you get a student participating who usually doesn’t participate!

  • Once you’ve gotten a few responses for that first image, ask students, “who has another reason why one of the others doesn’t belong?”

  • Scribe the student reasoning on the board and repeat the process until you’ve gotten multiple reasons for each image

The Most Overlooked Key To Success With WODB

The first time you do this structure with students, choose a non-math image set! Once students understand the structure, then use a math image set (like the one below). My favorite non-math image sets can be found here. This is often overlooked by math teachers in a hurry to get to math content - after all we do have so much to cover - but you will not see the massive increase in participation if you jump in with math. To get the engagement we dream of, we have to keep the math anxiety low and help students feel comfortable with the structure with a non-math image first. Do not skip this step!

Resources and Tools for Implementing the Strategy

  • The mecca of free WODB image sets is

  • If you want labeled, ready to use google slides, check out my image sets here.

  • My friend and Colleague over at Mona Math has a wonderful math teacher podcast, Honest Math Chat, and in this episode you can listen to both of us share why we love WODB and some secret pro tips!

Which One Doesn’t Belong is Only The Beginning

Wouldn’t it be wonderful if you had a toolbox of structures just like WODB that focus on student reasoning vs one correct answer? Well, you do! There are SIX Core Engagement Structures that do just that. PLUS they can all be introduced without math - to keep the anxiety low - and then bring the math in. These structures are so easy to implement that 100% of teachers who learn them report being able to implement them the very next day in their classrooms with a huge boost in engagement and participation of even their most apathetic, unmotivated, and challenging students. You can learn about all six in this Quick Guide.

And there you have it! The "Which One Doesn't Belong" strategy is like a secret math weapon we can all use in our classrooms to boost engagement of our most disengaged students. Imagine your classroom buzzing with curiosity and students teaming up to crack mathematical mysteries. WODB will get you there.

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