Not until college, when a few subjects eluded me. Chemistry, the second semester in particular, gave me a lot of trouble. Not even my lab grade could save me there. Ugh.
Calculus, where I had no clue what was going on. We did a lot of things on computers, and I never understood what the hell we were doing. I managed to scrape by somehow.
Genetics was also incomprehensible to me for at least half the semester. Our professor told us on the first day of class that most of us would be completely lost before the term was up, but that he’d take into consideration our lab work and effort. At first I had a good grasp of what we were learning, but about ⅔ through the semester I started to feel like I was taking a class in another language.