At my highschool it was down to the heirachy.
You had the "populars" who were always the prettiest/best looking. Usually the biggest bullies, the ones who routinely all smoked/drank/tried drugs and had underage sex.
Then came the "semi's" not the most popular, lower level bullies, not really hassled by anyone else who just kind of existed. Dabbled in sex and some drinking, maybe a bit of weed, and some smoked.
Then the "outcasts" the ones who get bullied, usually for being fat, smart, quiet/loners or not very attractive, or otherwise different, maybe with ND.
People stuck to their tier when it came to friends. Outcasts tended to band together so as to be with somebody rather than nobody, but they weren't really friends, didn't communicate or hang out after school, and went seperate ways once school was over.
College and beyond are much better as they're not mandatory, and are more interest basted, people meet likeminded people and better friendships.