I remember my AP Biology 2 class in high school. It still stands as one of the hardest classes I've taken which is saying something because in university I went out of my way to take the hardest classes available. Our teacher was proud of the fact that 97% of people who passed the class got a 5 on the AP exam. The AP exam was a walk in the park compared to that course.

That class was the exception rather than the rule, but I'll never forget it even if I've forgotten most of what I learned there.