Schools vary greatly, for various reasons.
Some students are just a rabble, but most are either reasonable or excellent.
Discipline policy is the good students are not supposed to suffer because of the bad ones, who should be dealt with on the spot or forwarded up the line.
It's important that parents are contacted as soon as there is a problem. Often, there is a home-based reason why the student is causing problems. For example, students whose parents are separated and the child floats between two homes sometimes turn up out of uniform or not having done homework because of the actions of parents. You do wonder what goes on in some homes.
Non-government schools seem more able to expel dangerous students than government ones.
I think the average person probably doesn't really understand what schooling is like nowdays. There is a huge amount of pastoral care because students are bringing personal problems to school with them.
Where I work, we have a reputation in the community for being a safe environment, unlike some other nearby schools. For example, I heard about a school where female staff were not allowed to do playground duty because it was too dangerous for them. I also heard about a school where many students had never learnt how to use knives and forks because they ate with their hands.
Of course, while we often focus on the problems, there are actually many students who are just great and making it.
My opinion is the most important thing students learn in school is not academic, but things like how to get along with others and get their own lives organized.

