In two studies, we assessed the effectiveness of a classroom activity designed to increase students' ability to think critically. This activity involved watching and discussing an infomercial that contained pseudoscientific claims, thus incorporating course material on good research design and critical thinking. In Study 1, we used a pretest-posttest design. After the activity, students were significantly more likely to correctly identify flaws in a series of claims. In Study 2, we compared the effectiveness of this activity to a traditional lecture. Participation in the activity was more effective at increasing students' ability to critically evaluate claims than the lecture. These results suggest that short-term interventions to increase critical thinking can be successful and can be made interesting for students.