At least, in terms of measuring how much students learn:

That conclusion invites another: students are, in essence, rewarding professors who award higher grades by giving them high ratings, and punishing professors who attempt to teach material in more depth by rating them poorly.

The article, from the Washington Post notes the most widespread alternative to evaluations, standardized tests:

In K-12 education, you have standardized tests, and those scores have never been more widely used in evaluating the value added by a teacher.

Because nothing ever goes wrong with those:

The district said the educators had distributed a detailed study guide after stealing a look at the state science test by “tubing” it — squeezing a test booklet, without breaking its paper seal, to form an open tube so that questions inside could be seen and used in the guide. The district invalidated students’ scores.