I like the below quote form this article:

Michele Pellizzari, an economics professor at the University of Geneva in Switzerland, has a more serious claim: that course evaluations may in fact measure, and thus motivate, the opposite of good teaching.

His experiment took place with students at the Bocconi University Department of Economics in Milan, Italy. There, students are given a cognitive test on entry, which establishes their basic aptitude, and they are randomly assigned to professors.

The paper compared the student evaluations of a particular professor to another measure of teacher quality: how those students performed in a subsequent course. In other words, if I have Dr. Muccio in Microeconomics I, what’s my grade next year in Macroeconomics II?

Here’s what he found. The better the professors were, as measured by their students’ grades in later classes, the lower their ratings from students.

Cheers.