Researchers have yet to examine whether discussion group size affects student performance in an interteaching-based course. In the current study, we addressed this question by manipulating discussion group size (smaller groups of 2 students vs. larger groups of 4 students) across 2 sections of an undergraduate psychology course. We found no significant differences between the sections on 6 unit exams, on a cumulative final exam, and in the total number of points earned across the semester. A sample preparation guide from the course is also presented. (Contains 1 table, 1 figure, and 1 footnote.)