Which One Doesn’t Belong?

One of my favorite activities I did regularly with my 2nd graders in the past couple months was inspired by Christopher Danielson’s “Which One Doesn’t Belong?” posters.

These are an incredible resource! Find them here.

The posters came in a set of 8 – a perfect amount for us to explore one per remaining week of school. I found some unused magnetic name tags and decided on this set up.

I had no idea what was going to happen – I gave no verbal directions (only vaguely pointing out we had something “new” in our classroom). It took a couple days, but students did start to engage.

Students’ thinking about the equilateral triangle not being “stretched” shows that they’re beginning to think about the relative size of angles.

Each week, I would put up a new poster on Monday and we would have a whole-class discussion about our ideas on Friday.

As we continued with this routine week after week, students’ reasoning became more sophisticated and their engagement increased as well – students would sneakily move their name to a shape during circle times and transitions. They would congregate around the poster, asking about and pushing back on each other’s choices.

Nobody chose the blue square because it was the most “regular”. What might make a shape “regular”? Do some properties of shapes matter more than others?

Here are some of my favorite noticings and conversations we had.

  • The top right hexagon can be turned into a drawing of a cube by drawing three lines. (Do you see it?)
  • The other three hexagons can be “squished” a bit to all look the same. (What does this tell us about angles?)
  • The top left shape (in the poster on the right) could be straightened out into a very long, skinny rectangle.
  • What is a shape? Are letters shapes? Is everything a shape? Do all shapes have names?
  • What is a polygon? Can we come up with a definition from this poster (below)? Could we explain it to a Kindergartener?
    • Ideas – a polygon might be: a shape with a lot of sides, a shape with at least 4 sides, a shape with any number of sides that are “line segments”.
The top left doesn’t belong “because it is a square and I don’t know what a polygon is but I know it is not a square!”

Now for some questions moving forward…

  • How might you use these posters in your classroom the whole year? With younger kids? Older?
  • How might you support students to create their own WODB images, perhaps moving beyond just shapes?

How do you use WODB in your classroom?

Let me know in the comments!

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