Saturday, November 28, 2015

Which One Doesn't Belong?

After returning from the NCTM Conference in Nashville, I decided to do this activity called "Which One Doesn't Belong? as part of my First Five (which is what I call my bell ringer). This activity gives students either four numbers, graphs, pictures, etc. and asks students to explain with reasoning which one doesn't belong. The nice part about this activity is that it allows for divergent paths of thinking as well as allow for students to justify and explain their reasoning.

Here is the first one I did with my first block geometry class. 

Students had several reasons why they chose their particular shape. 
  • "I think it is the hexagon since all of the other figures are triangles." 
  • "I think that it's the shaded in triangle because all of the others are not shaded in." 
  • I think that it is the triangle in the upper left hand corner because it looks smaller." 

This allowed for my students to be able to justify and defend their answers. I told students beforehand that there was not one right or wrong answer as long as they could justify their answers. 

I then gave this problem to my Algebra II class. 

Here are some of the students' thoughts. 
  • I think that it is 9 because it is the only single digit number. 
  • I think that it is 43 because it is the only prime number. 
  • I think that it is 16 because it is the only even number. 
  • I think that it is 43 because 9, 16, and 25 are all perfect squares. 
  • I think that it is 43 because you can take the square root of 9, 16, and 25 and get a whole number

I want to say that I had so much success with this activity that I will definitely plan on using it again I even did a tweet out to the Math Twitter Blogosphere about it :) 

So I encourage you to use this activity with your students. The website is Which One Doesn't Belong?

So, with that, I hope you have a great rest of your Thanksgiving Holiday and rest up strong for three more weeks until the Christmas/Winter Break!!! 


  1. I just recently started the WODB activity with my Grade 6 Special Education math students. We also started with the first shape set. It was very interesting to hear them talk about their ideas--and it was really 'freeing' for them to know up front that I didn't have a 'right' or 'wrong' answer. They were able to share their ideas in a safe place and are learning to talk together about math in a way they haven't before.

    1. Hi Melissa! I found about WODB at the NCTM Conference in Nashville. I plan on using it a lot more next semester. I had never thought about that perspective of it being "freeing" for students because there is not necessarily a right or wrong answer. I was proud of my kids when we did this. I may have to write a blog post about it next semester with some more student thoughts. Thanks for commenting!

  2. Hello! This post was recommended for MTBoS 2015: a collection of people's favorite blog posts of the year. We would like to publish an edited volume of the posts and use the money raised toward a scholarship for TMC. Please let us know by responding via email to whether or not you grant us permission to include your post. Thank you, Tina and Lani.

    1. I just sent an email back saying that I grant permission to include my post, and I thank you so much for your comment and the honor!


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