I went to High School in a suburb of Phoenixwith a very narrow income range. The difference between "poor" kids and "rich" kids (which really refers to their parent's income, obviously) was probably not greater than a factor of 2. So in todays money (I have no clue what the numbers were then), say a middleclass family with two working parents, makes about $100k, I bet there were some families that made $75k (not poor by anyones standards) and some that made $150k (not rich by anyones standards) but that's probably the extent of the range (again, in today's money).
So the divisions were not economic, but style or interest. We had punks, metal/rockers, new wavers, stoners, jocks and preppys. And there was plenty of crossover between the groups. The jocks weren't stereotypical "dumb jocks", they were all in the College prep classes, because the all had hopes of going on to college athletics. They were all friendly with everyone, some of them liked metal, some like top 40, so there was that music cross over too. Everyone bought drugs from the stoners, so they were well liked. A lot of the metal heads and punks were in local bands that would play at the parties thrown by the preppies and the jocks, so we were popular with them (that's where I fit in. I was in metal bands all through Jr High and High School, and a few years after).
I graduated in a class of 1000 from a school with 3000 students in 3 grades (9th graders went to Jr High at the time, so it ws just 10-12) and there just wasn't any division based on anything other than your individual personality. If you were cool, then you were cool with everyone. If you were a dick, then everyone hated you. But I had a good time in HS. Then I went on college, and had a good time there too. Maybe I was lucky to grow up in the suburbs in a relatively new community where there wasn't 100+ years of history creating those divides. I bet no family at the time lived in a house older than about 15 years, from the particular neighborhoods that fed into my high school.