I really wanted the fire emblem edition, but I think that design only applies in the old 3ds models :c
high school is from year 7 to year 11, which I think in america that would be 6th grade to 10th grade. I'm currently in year 13, which is the 2nd and final year of what we call 'sixth form', which is basically kinda like a senior high school (or 12th grade, if that grade exists??) in sixth form we do something called 'a-levels', which is the highest form of education before university. you choose four a-level subjects at the start of year 12, do exams in the summer, then normally you drop one of the subjects you were doing in year 12 and take the other three onto year 13, where the content is much harder. your grades from year 12 and 13 average out to become your a-level grades in the end, in a form of As and Bs and so on.
There's a bit more to it than that, but I thought I would stop there because I just realised I just created a pretty thick wall of text aha.. you do get the idea though, right?