Professors allow students to pick their own grade

Interesting. The article itself does not add much insight from the professor (Dr. Melissa González) since she didn't respond to requests for comments, so it is based on a research paper she cited and an email she sent to potential students.

If you're interested in these type of experiments, you should read some of the books by behavioral economics professor Dr. Dan Ariely. He has several talks online as well. I'm partial to his first book on this topic, Predictably Irrational, but he has several other books exploring human behavior.