Which One Doesn't Belong? Perfect for Morning Time Math

Here is one of our favorite math picture books to read during morning time, when I have all my kids together. 

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Which One Doesn't Belong? is perfect for sparking math discussions with multi-age groups. Which one doesn't belong? It's a trick question! Each shape could be the right answer because each shape is different from the others in some way.

Which One Doesn't Belong? provides a natural way to introduce mathematical vocabulary (such as vertex and reflex angle) as well as geometric concepts (such as the attributes of a polygon). It is perfect to read with a wide span of ages because every child can observe and engage, whether they know the official mathematical vocabulary/concept or not. I like to do just one or two pages at a time. For an extra challenge, try creating your own set.

There is a teacher's guide that is not necessary in order to enjoy the book but full of great ideas. For example, it describes how to create your own Which One Doesn't Belong set. It provides in-depth discussions of the mathematical concepts that arise from each of the shape sets in the book. Plus it has an "answer key" - in case you can't figure out how a certain shape is different. 

You can find additional Which One Doesn't Belong? prompts on the Which One Doesn't Belong? website (includes not just sets of shapes, but number sets and graph sets!), or check out the twitter account @WODBMath or twitter hashtag #wodb. You might also want to try creating some sets yourself! I've also found some fun ones just searching Google images for "which one doesn't belong?"

The same author recently published How Many? which playfully explores number and counting. I'm looking forward to reading that one with my kids soon.


  1. Thanks! Ordered the student/teacher set! So glad you shared this on Instagram!


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