Which One Doesn't Belong?

Support students to reason mathematically by determining which figure, diagram, graph, or expression does not belong
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About This Strategy

In this strategy, students determine which items belong or do not belong in a group. You present students with four figures, diagrams, graphs, or expressions and ask the students to determine which one doesn't belong. You should strategically pick figures, diagrams, graphs, or expressions that could each not belong for different reasons. The objective of this activity is to support students to justify their thinking using precise mathematical terms.

Plan It

Prior to implementing this routine, it is important that you strategically plan for implementation by completing the following:

  1. Find a "Which One Doesn't Belong" example or create four figures, diagrams, graphs, or expressions that align with the current content you are teaching. 

    • There are many free examples on the internet if you search "Which One Doesn't Belong?"

  2. If you are creating your own group of four figures, diagrams, graphs, or expressions, be sure to pick figures, diagrams, graphs, or expressions that could each not belong to the group due to different reasons. This will support students to justify their thinking.
    • You do not need to only have four items. The number of figures can be changed based on your individual situation and lesson goals.
  3. Decide how you will introduce this routine to students. Consider modeling this for students and providing opportunities to practice in low-stakes way.

Practice It

Now that you have reviewed the activity and routine or created one, it is time to implement it with students.  

  1. Model for your students by showing them how you would determine which item might not belong in a group of four.

  2. Show the students four figures, diagrams, graphs, or expressions and ask the students to respond verbally or in writing to the question, "Which one doesn't belong?"

    • Be sure to ask students to justify their answers by responding to questions like, "Why?" Or, "How do you know that?"

    • Remind students to be precise in their explanations.

  3. Consistently use this activity as a warm up to support students to reason mathematically and justify their thinking, or as a lesson closer in order to assess students’ comprehension of new material.

Reflect and Refine

After you begin implementing this routine, consider the following:

  • What went well? What was challenging? 
  • Did this routine your support students to reason mathematically?
  • Did your students use precise math vocabulary?
  • What additional supports should you include during the next round?

After engaging in reflection, determine any changes and go through the planning and implementation steps again. 

Open Up Resources Math

Which One Doesn't Belong is an instructional routine in the Open Up Resources math curriculum that is used during the warm up activities. Prior to beginning, review the overview of this routine and specific examples located in the resource section below. You will need a to create a free login to access these resources.

IM K-5 Math

Which One Doesn't Belong is an instructional routine in the IM K-5 Math curriculum that is used during the warm up activities. Prior to beginning, review the overview of this routine and specific examples located in the resource section below. You will need a to create a free login to access these resources.

EL Modification

Provide English Learners with sentence starters to support them to formulate their responses. Consult the "Accountable and Academic Student Talk Stems" strategy in the BetterLesson Lab for resources or for more information about how to use talk stems with students.

BetterLesson Lessons

If you'd like to learn more about implementing Which One Doesn't Belong, review the lesson below.