When I was in middle school, it was a school which was built for 500 students. We had an enrollment of about 1500. The teachers were all incredibly burnt-out, and the principal only cared about trying to maintain some semblance of order. At the start of the day, before the bell officially rung to start classes, all 6th and 7th grade students were *required* to assemble in the main lobby -- which was really only built to house 100 people or so. Instead, you had about 1,000 kids packed in like sardines. The halls off the main lobby were blocked with chain-link doors which were manned by teachers and only opened when the 1st bell rang. I still lovingly refer to it as "William Golding Junior High".
Needless to say, it was an environment where bullying and fighting were not only ingrained and persistent, they were encouraged. If a fight broke out in the lobby, the larger 7th graders would form a ring around it, and
charge admission fees if 6th graders wanted to watch. And they had no shortage of takers. The teachers rarely managed to push through the crowds in time to stop a fight, so after a while they just stopped trying.
I once watched two girls get into a fight near the buses at the end of the day, and one pulled out a three-foot length of chain and began whipping it at the other girl's head, who took off running and rolling UNDER the parked buses to try and get away. I got into a couple of fights myself, usually by accident when I just snapped and verbally retaliated against somebody, who then escalated it.
The buses tended to be driven by haggard little old ladies who would yell and curse at us, but did little to intervene. This lead to such fun games as "Let's dogpile 20 people on THAT guy!". They only did that to me once. I was scrawny, almost skeletal back then. I started to black out from the combined weight of all these jackasses crushing my chest to the floor, and then the next thing I knew I was pinning one of my "friends" to the roof of the bus by his throat, and everybody was cowering. Apparently I snapped and went full-bore Viking berserker. Too bad people didn't tote video camera around back then...probably could have been a YouTube star.
The one good side-effect of that incident is that I actually didn't get bullied all that much in middle school, because I had established a reputation of being somewhat psychotic. Downside is that I didn't have a lot of friends either. And certainly no "relationships".
Unsurprisingly, I have a very strong urge to homeschool my daughter when it comes time for middle school. I know my experience was a bit extreme, even for US schools, but IMHO that age range (11-15) is when kids are the absolute worst monsters possible -- they're old enough that they no longer have an inherent fear/respect of grown-ups and authority figures, and most haven't matured enough to have developed empathy and morality. Add to that a psychological need for group identity, and the onset of puberty.....it's not a pretty thing.
And from my own experience, girls are worse than boys. Boys are physically abusive to each other, but it's like infighting in a pack of dogs. It's all about establishing the alpha, and then everything is mostly okay. Girls are psychologically abusive, and (again, this is purely IMHO) do more things out of sheer malice than for fighting for position in a social hierarchy (although jockeying for inclusion in a clique is definitely part of it)