Well I can only speak for my children's (primary) school but :
Violent and disruptive kids are put in a "nurture room" where they are pandered to for the whole day rather than being punished.
Violent and disruptive kids are allowed to slam the classroom door over and over again as hard as they like to "get rid of their anger".
Violent and disruptive kids are allowed to sit and eat Gregg's in class next to the other children who are getting on with their work - because eating Gregg's apparently "calms them down".
Violent and disruptive kids are allowed to skip tests (SAT's etc) because the school know they'll bring down the school's average score.
Violent and disruptive kids are given certificates and rewards when they do one tiny thing decently - whilst the regularly well behaved children are overlooked for such treats.
Violent and disruptive children aren't allowed to be restrained when they are having a melt down and assaulting other other children, because their parents then come into school complaining that the teacher has hurt their child whilst trying to stop them hurting another.
Violent and disruptive kids are allowed to use the toilet whenever they want while the other children have to ask the teacher or wait until break time.
Violent and disruptive kids are allowed to rip up textbooks, throw things at the teacher, and tip out every single one of the work drawers with no consequence.
I could go on and on and on here but you get the jist. The brats are mollycodled and the well behaved, decent, hard working children are overlooked and pushed to the side. This is happening across all different year group's in my children's school (I have 4 all primary age) and all of them have been a victim of assault and/or bullying by these kids that cause problems on a delay basis. My children see the preferential treatment that they are given and quite rightly question it.
My son's bully got punished by "missing his lunchtime break" but was allowed to pick a friend to stay in class with him so he had someone to play with! This boy is 11 years old and knows exactly what he's doing. The school is full of them, getting older and bigger and stronger each year, working their way up to year 6 where they are allowed to continue to do what they want.
It would be laughable if it didn't infuriate me.
If I had the time and means to home school, I would.