When I saw this I thought you were going to give me a nudge about another topic (but I'm keeping out of that now as it's harmless I suppose and raises some important points).
Anyway, AQA is one of a number of examining boards.
Have you seen this part of their site?
http://web.aqa.org.uk...iew.php?id=02&prev=02
They were popular because of their modular exams. However the government has said that the modular exams are being phased out, so get in quick and check that you can finish them in time if you want to be fully modular. There's nothing wrong with a linear approach though.
Sorry I don't know about costs at an adult class.