Background: Increasing students' ability to think critically allows them to engage more fully with psychology material. Objective: The current study used a critical thinking assignment called PsychBusters to examine critical thinking and interest in psychology in two sections of introductory psychology designated for first-year psychology majors. Method: The experimental section completed two PsychBusters presentations including a poster presentation. The control course section also completed poster presentations but did not do the PsychBusters assignment. For both sections, critical thinking skills and levels of interest in psychology were measured at the start and end of the semester. Results: Students in both sections maintained a high interest in psychology across the semester. The section that worked on the PsychBusters misconception assignment had similar critical thinking skills as the control at the start of the semester but had higher scores at the posttest. Conclusion: Assignments that direct students to focus on critical thinking may not improve one's interest in psychology. However, class assignments that hone critical thinking skills should be integrated into psychology courses with the aim of improving students' reasoning. Teaching Implications: The development of critical thinking skills in psychology majors should start early in the curriculum.