Which one Doesn't Belong?
Routine Description

A classroom routine built to support WODB Group Activities:

1. Tell students that we will be doing an activity together called Which One Doesn’t Belong. “We are doing this activity to think like mathematicians, to look at differences between numbers.” Tell students that there are no wrong answers here, that we are interested in the arguments students will use to select their answer.
2. Give students about 1 minute to look at the four numbers, choose one of them that does not belong, and to explain why it doesn’t belong. This can be done on paper or in the students’ heads.
3. Ask students to share which one they selected and their reason for selecting it with a partner. Listen to students as they share their arguments and select one student to present an argument for each number.
4. Ask students to present their arguments for why each number doesn’t belong. As students present, if appropriate, point at exactly what they are talking about as they share. Ask another student to restate what the first student shared, and then add annotation or a record of what the argument is. Repeat this process for all four mathematical objects.
5. Ask students to write a reflection to share with a partner about what is important to pay attention to, the next time they compare different numbers.

For more information on Which One Doesn’t Belong, see https://wodb.ca/.