1. You are just starting year 12. Some subjects might be different from what you expect them to be like. The reason I say don't drop to 11u that fast is because if you figure that EE1 is a shit, boring topic this year and you would rather have done eco, well you can't change that. If I dropped at the beginning of y12, I would've dropped EE1 + EE2 first choice - which luckily I didn't, because I ended up doing better in it than a couple of my other ones. Our school recommended 12u for the first term (compulsory for the first 3 weeks) for this reason - just to try it out and make sure you weren't going to regret it.
2. Sometimes you just get unlucky. You have a bad day, or whatever.
a) I know we had to do an amended task in a subject because someone complained about it (who would've guessed?), and although I had done well in the original one, I screwed up the amended 'cos they structured it differently (the complaint was only about 1 section), and reduced the time limit we had to finish it in, which I wasn't used to since we had never done a test like that. I dropped 40 ranks in that task, and although I topped trials, it was just a bitch 'cos I could've topped the course instead of dropping 7 overall ranks.
b) I know a girl who missed the last page of her exam 'cos the pages were stuck together or something, and we weren't told the exact format of the paper (i.e. comprehension questions at the end) = -5 out of 40 marks.