Research on minimal groups demonstrates that arbitrarily creating 2 groups leads to the development of in-group favoritism. Experiments using the minimal groups paradigm show students how easily in-group biases can be created simply by categorizing others. This article describes an in-class activity that demonstrates the power of categorization. Students completed a minimal groups experiment either before or after viewing the video A Class Divided. Regardless of when they viewed the video, students rated their arbitrarily assigned in-group more positively and less negatively than their out-group. These findings spurred lively discussion about the possible relation among categorization, discrimination, and prejudice. Students enjoyed the activity and indicated that it was a valuable technique for demonstrating in-group bias.