maths A-level: structure classes

Could anyone tell me how Maths are taught in Y12?
1. Get the students one subject (like calculus) every class until that subject is finished or do they e.g. have calculus on two specific days in the week and another subject like algebra on two other days?
2. What subjects (Maths) are taught in the first weeks of the school year?
3. Are there group assignments for Maths?

I am writing a book that is partly set in Wales and I want to make it realistic. That is pretty hard because, as a Belgian, I am not very familiar with the school system.

Thanks for your help!