I've been stuck with so many incompetent teachers (either at teaching or the subject material) in my school years. I just use my general knowledge to get by, and it works. I find myself though, having to turn around and teach someone something a teacher just taught us quite often. That bothers me a lot. A teacher is paid to TEACH.
I guess I just got lucky, and am able to "wing" test/quizzes/classes. I do read a lot online though which probably helps.
O and right now I'm in basically a prepatory chemistry class that most people take in my school. I'm taking AP Chemistry next year. My teacher though is incompetent in the material. She reads word for word what one of the other chemistry teachers gives her, and what is in her "teaching book". It drives me crazy because I need to constantly explain things to other people.