Student evaluations are a poor indicator of professor performance. The good news is that college students often reward instructors who teach well. The bad news is that students often conflate good instruction with pleasant ambience and low expectations. As a result they also reward instructors who grade easily, require little work, are glib and chatty, wear nice clothes, and are physically attractive. It’s generally impossible to separate all these factors in an evaluation. Plus, students will penalize demanding professors or professors who have given them a bad grade, regardless of the quality of instruction that a professor provides. In the end, deans and tenure committees are using bad data to evaluate professor performance, while professors feel pressure to grade easier and reduce workloads to receive higher evaluations.