Which One Doesn’t Belong – A Math Class Favorite!

I am obsessed with the game Which One Doesn’t Belong? (WODB for short). I started playing with my classes while virtual teaching through the pandemic. We started once a week and by the end of the year, my students were begging to play daily!

WODB is often played through a mathematical lens, usually presented to students as a math class opener/bellringer activity and for good reason. This simple yet powerful activity hits many of the standards for mathematical practices:

• MP1 Make sense of problems and persevere in solving them.
• MP2 Reason abstractly and quantitatively.
• MP3 Construct viable arguments and critique the reasoning of others.
• MP6 Attend to precision.
• MP7 Look for and make use of structure.

WODB Game Basics

Inspired by Sesame Street’s “One of these things is not like the others”, mathematician Christopher Danielson wrote the book Which One Doesn’t Belong using shapes and the rest is history. You can find him over on the Talking Math With Kids blog. He’s a wonderful teacher dad full of mathematical knowledge!

In a typical WODB prompt, students are asked to look at four items and share out their reasoning as to which one doesn’t belong. The kicker? There’s always more than one reasonable answer! In fact, the beauty in this game is that there are no wrong answers, so long as the student’s reasoning makes sense. The focus is not so much on the item chosen, but moreso on the student’s ability to communicate his/her decision making skills.

Benefits of Playing

Because all the answer choices can be right, students naturally shift their focus away from being correct to sound justifications and viable arguments. WODB is a low floor, high ceiling activity. The game is easy to play and the discourse endless! If I keep my mouth shut long enough to allow think time, even my shyest mathematicians have the confidence to boldly contribute to the class discussion.

It is in the dialogue that follows their WODB selection where the magic really happens. Some kids are very short in their explanations, often speaking in generalized terms. Others are expanding on previously shared ideas, using specific academic vocabulary and detail to further prove their point.

Mathematics aside, WODB is a great language activity. Kids that won’t or can’t write a five paragraph persuasive essay are rattling off one reason after another for five minutes straight. The true purpose of these prompts is to stimulate the mind, build grit, establish a growth mindset, and generate curiosity. It’s amazing to see all these pieces come together!

A Word of Caution

While many treat WODB as a math game, I would not necessarily introduce it to students in this manner. Kids as young as first and second grade often have already begun to associate math with feelings of fear and negativity. Cognitive scientist and Barnard College President Sian Leah Beilock found that nearly half of students indicate they are “moderately nervous” to “very, very nervous” about math. All that bad energy triggers a flight or freeze response within most people. As a result, the working memory is negatively impacted, an important piece of the brain when solving problems.

I started incorporating WODB into my morning meeting routine. We start the year with one a week and build from there. There are many mathematical prompts involving numbers and shapes, but I don’t start there. In fact, I ended up creating my own set of WODB prompts that had nothing to do with math.. or did they?

When you first play the game, some students feel trapped. Had I played WODB as a child, I would have been THAT kid. I do much better with clear-cut expectations. Kids like me will panic: How could there be no one right answer? There’s always a right answer!

For other kids, however, the open-ended aspect of WODB will be heaven! Regardless of their perceived mathematical ability, you’ll have students willingly engage in logic and reasoning with peers because the pressure is off to come up with a particular right answer.

Where’s the Answer Key?

Please note that WODB activity sets like the one listed in my TpT store do not include an answer key since the prompts do not have a single correct answer. The graphics used are designed to be interpreted in a variety of different ways in an attempt to spark mathematical thinking and discussion.

Real talk: some of the sets I personally created do not lend themselves to having all four choices be viable solutions… at least, not ones that I’ve figured out! Still, I feel I’ve done a pretty good job of including at least two but usually more options as the “correct” response.

WODB Examples

Here are two sample prompts from my morning meeting game set. Which one doesn’t belong?

ACTIONABLE STEPS: Let us know in the comments below: which one doesn’t belong? More importantly, tell us WHY!