Hey, I went on the same type of Summer school last year so I hope I can help you out. Like you, I was the first one ever from my school to go on one of these summer schools - my maths teacher didn't even know what it was - so don't worry about having to ask questions. My sessions were on combinatorics, which is a part of maths you don't really get to study until AS usually, so no-one really has a clue what's going on at first. The idea behind the sessions though isn't to learn the actual content, but to get used to asking questions and solving them yourself, and while it's really hard it's also a lot of fun and everyone else is in the same boat. In terms of dress code, it's a lot more chill than they make it out to be on the letter - I wouldn't get away with wearing what I wore to the summer school to my sixth form - so as long as you're decent and vaguely smart it's fine. If you're looking for a guideline, I wore various semi-decent pairs of jeans and very basic t shirts all week, and I didn't look at all out of place, so there's no need for a suit or anything like that. If you have any more questions, feel free to ask - a few of my friends from my summer school are going to be on your summer school as a 'senior' student (basically just there to help out and provide a bit of support should anyone need it) so you're in excellent hands when you get there.