I would guess the vast majority of people in my highschool were in the top fourth of income in America (including my family, we were well off but not super rich because my dad was in the military and then a commercial pilot and my mom was a teacher). I'm sure other people have different experiences but waaaayyyy more than the national average of people from my highschool went to college and I can tell you that while it was a decent school it was not filled with geniuses. It's why I think a large amount of the reason people go to college is cultural and that to many people college ends up being more of a symbol of status than a intellectual achievement.