For GCSE, I got 4B's and 5C's. I was expected to get some A's and possibly an A* but the teachers didn't guide me right.
Music teacher for example (what I'm good at), couldn't teach, so didnt' know what would come up in exam.
I.T, I was told after I had checked with him, after getting it back, that it wasn't really the right thing to do to get a high mark.
Art, I couldn't do drawing because he said I wouldn't get enough marks for drawing alone, so said to do Water colour, and I can't do that, and didn't get it finished! I suck at any other kind of art, except pencil drawing.
Science, I got B's in, but could have got better again, because I never got told you could rework the coursework to get higher marks based on teachers help!
So yeah, I could have got higher grades
In college though in my E-media course, I got 3 distinctions though (the best you can get), which I was happy about.