I had tested out of first quarter chemistry with the advice I attend class (I went to one). I did OK second quarter and then made a D third. That's the only D I ever made. I figured I should change my major, but I had already signed up for soph courses, and I was too lazy to change. So, I'm in org chem with a bunch of quasi-premed types, and the professor, one M. Gary Newton, was excellent. He made it interesting, to me. We started with 180, people sitting in the aisles until after the first test, and ended the year with about 30. So, that one professor surely changed my course in life. I wrote a letter to the department when I heard he had passed.
Coursework is a lot easier if you're interested.