That's impressive. But I think we're working with different notions of suburban. For a suburban high school to have a graduating class of 500, you were presumably around a large population center? Where I grew up, that was the size of the high schools in the city (of about 120k).

My school district, an amalgamation of suburban enclaves and small towns, only had about a third of that. I think being close to a larger city means probably a more sophisticated suburban population (I don't think I'd ever met anyone who'd been to an Ivy-ish school prior to college) and larger schools, which allows for more stratified educational tracks.

All depends on how big the regions are and how many schools they build. My regional suburbia high school had 350 per class.

Am I misinterpreting, 350 in one classroom, or does class here mean what I'd think of as 'subject' ?

It means what you probably think of as "year".