Just thought I should add that in my AS mocks last year I got CDEU(I had a lot of time off before the mocks due to personal reasons but tried my best to catch up) and in the real exams I got CCDE, which is poor I agree but I worked harder than ever to improve my grades and I was ill around the mocks as wel, not that I'm using that as an excuse..
My highest mock grade was English Lang lit but I hated it, and ended up with a low E and dropped it before a2.
I've just done my a2 mocks and got a CDDE (retaking a module of as psychology) I'm not saying I'm a success story but I've never been a success with exams etc.... But my number one factor difference between the two years was my attendance, I havent had a single day off during a2, whereas AS my attendance was shocking... But yeah I'm an average student, you can get from E in the mocks up to a C like I did,but equally as likely to get a C down to a low E. It's all about how much work you put into it