Which One Doesn’t Belong is one of my favorite routines to use with students. Students choose which one they think does not belong from a group of images. The most important thing is that they explain why they believe that particular image does not belong. And anything goes. An example from the image above would be I think that the bottom right does not belong because it is the only one that is green. Students also need to be thoughtful that their explanation only works for that particular image. If I said that the bottom right was outlined in red, that would also apply to two other images so that I could not be why just that image does not belong.
The reason I like this routine so much is because all students have the opportunity to share how they see the images and I learn just as much from them sharing. Often, I make assumptions about what students know and what they do not know. By using Which One Doesn’t Belong, those assumptions are usually proven incorrect and I am surprised by what they do remember. Often, vocabulary that they do know comes out and leads to a discussion about what that particular word really does mean. In the end, students realize that each one of the images does not belong for some reason as well as realizing that they all have something in common.
When I introduction Which One Doesn’t Belong, I like to start with ones that are not mathematical in focus so that students are worried about whether or not they have the correct answer. Once they have the idea of Which One Doesn’t Belong, then we start to do ones that are focused on the math that they are studying. Here’s one that I did in a classroom where you can see all the student thinking:
You can find more ideas for Which One Doesn’t Belong here.
Where’s the math? For Which One Doesn’t Belong, student have to construct viable arguments and critique the reasoning of others. Once students understand the routine, then you can choose the math that is relevant to them. For first grade, that might be coins. For high school, they could compare graphs of different polynomials.
What grade level? K-12+
Ideas for Remote Teaching
- Synchronous Teaching – This idea was shared by Sara Van Der Werf at NCSM’s Virtual Conference. You can have students go and grab a household item for which one they think doesn’t belong. Using the Which One Doesn’t Belong from the top, if you think that the heart doesn’t belong, then go and grab a fork. If you think the star doesn’t belong, go and grab a knife…and so on. And then have students share reasons why.
- Asynchronous Teaching – Students could share on a GoogleDoc why each one does not belong.
- Paper – Have students ask members of the family why they think each one does not belong and have them record it.
- Homework – Students could create their own Which One Doesn’t Belong focused on a particular topic.
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Mathematical Thinking In Wuttig's World 