An online collection of visual math problems for students in Grade K–12, “Which One Doesn’t Belong” provides colourful image groups and encourages students to think deeply about which image should not be in the set, also requiring them to apply mathematical reasoning skills and encouraging them to communicate their perspectives using mathematical language. The categories of images lend themselves well as an introductory activity to a math lesson on the topic of study. In the classroom, teachers may use the resource as a whole-class activity or in small-group work to spark creative thinking and initiate student discussions, inviting them to talk with peers and defend their ideas.