The community has to do its part. Children need rules. That's one of the ways they learn. A youngster who is violent or disruptive needs a different setting. That can be a separate special school or a separate setting within the same school.
Smaller things matter, too.
Lateness, for example. I remember very well what happened a couple of years ago in a tough high school in the Bronx. There was a discipline code, but it was not consistently enforced, and the place was out of control. So when a new principal came on the scene, the teachers went to him and pressed him to do something. Together, they worked out a plan.