Wow, Comrade's answer was such a good read. Hello again!
:/ I can't even imagine a high school like yours, Maddie. It just sounds so bleak, how can kids excel in a gender-segregated environment I don't even know... My high school years were split between Dubai (-till Year 11) and my final two years in NZ as an exchange student. Both, of these schools were fairly diverse but the high school in Dubai was the most culturally diverse out of the two. The circle of friends I hung out with were Polish, Cantonese and English. Dubai is a very multi-cultural city in itself, the expat:local ratio is crazy and the school I went to had lots of kids whose parents (including mine) were working for companies that migrate people from overseas and set up their families with healthcare plans, education, housing things like that. So it was a bit out of the norm. But my high school was filled with kids that were mostly from European countries, India, Japan, Hong Kong and a small amount from the US (not many Americans though because the school was British curriculum).
As for politically diverse, it didn't really crop up in everyday conversations but I remember during English we'd discuss a lot about it (ex. we had to annotate and critique a classified clipping and it said "wanted: white, male preferably European or US educated for a firm"). There were lots of people who took the subject and conversations like this would always come up. Also during History, I can't tell you how many times we've wasted lessons getting distracted and talking about politics, especially living in a country like UAE where it's tax-free, no government support (no healthcare benefits or anything like that) and everyone is an expat doesn't matter if you've lived there all your life you can't become a citizen. There's definitely been discussions on how the country runs itself with expats but doesn't recognize them.
Same as yours with economically diverse, mostly above average to rich. I can't really remember subcultures or many cliques actually, it was a really tiny school (the Yr12 and 13s were a group of 30 students) loads of people would come and go so once you got attached to someone they'd probably leave within six months. We were all a massive group actually, our break was for 1 hour and all the guys would play football then. Then the girls would be split in whatever they wanted to do during that break (mostly I was in the music room with my friends because it was quiet there, the teacher had some really neat stories to tell and she'd let us play the instruments if we wanted to practice. During classes though we'd all be mixed according to the subjects we wanted but one way or the other we interacted with anyone and everyone. The teachers made sure it was that way.
That's about it, really. Sadly I don't really have many fun stories to tell about my high school years in NZ because the years just feel like they blended into one and it was an extremely stressful time (picking universities and what I wanted to do with my life etc). It definitely was an eye-opener on how massive a school can be but so alienating at the same time?