Students are paired up for this activity. Each partner must solve a set of questions. The answer for each question number is the same for both partners but the problem is different. If a student gets a different answer then their partner, they must look at their work and their partner's work to determine where the mistake was made. This is a very easy to work with template. This activity can be adapted to many subjects. You can also view my comparing and ordering integers partner activity to get a better idea of what this activity can look like.