Where class size really matters: Class size and student ratings of instructor effectiveness

We examine the impact of class size on student evaluations of instructor performance using data on all economics classes offered at the University of California, Santa Barbara from Fall 1997 to Spring 2004. A particular strength of this data is the opportunity to control for both instructor and course fixed effects. In contrast to the literature examining class size effects on test-based outcomes—where results can vary considerably across specifications—we find a large, highly significant, and nonlinear negative impact of class size on student evaluations of instructor effectiveness that is highly robust to the inclusion of course and instructor fixed effects.