This resource is fantastic to use to develop critical thinking and problem solving in students. Students looks at a set of numbers or pictures and deduce which one doesn't belong. The goal is to have students justify their choice, as there is always more than one way to solve the challenges. There are 30 different challenges, 10 of which involve number sets, 10 shape sets, and 10 additional incomplete sets. The sets are excellent for differentiation, as there are several entry points to each of the sets.