Well, in my school, anyone who wants to do A-level maths has to have done GCSE Add Maths, which was a toughie, because I wanted to do it, and didn't particuarily like maths when I was 13. But I was allowed to do it on the condition I got a high A* at GCSE, and I can see the difference. In a class of 22, I am the only person without GCSE Add Maths, and although my teachers explain the concepts everyone else knows, she would have to explain it in mroe detail if the entire class came from just single GCSE. But thats just my school and sixth form,probably different for others.