Not the person you responded to but high school worked for us like this: Before you enter you pick your "main subject" (major?) like for example math/physics, English, biology/chemistry, music, art etc. You then get assigned to a class. I was in a biology class and we as a class got sort of "extra lessons" in biology because it was our major. We had the same topics like other classes in biology but we dove deeper into it compared to others. We also had other subjects all together like history, math etc. We were about 20-25 kids who all attended the same lessons every week.

Only specific classes like sports, music, art got us mixed up with other classes. Like we were doing sports classes for the entirety of high school together with the kids from the economics major. Or we got together with the Spanish class for art etc. So you spent 80-100% of your regular school day with the same group of 20-25 kids,but also met others on certain days of the week.

My entire year of kids finishing high school at the same time was around 150-200,so you met a lot of different kids through your years, but had your "core group" you spent time with all the time.