1. When a parent withdraws their kid from a school that's not doing the job, the parent's money GOES WITH THEM to whatever other school they ultimately choose.
2. If any kid in any class disrupts the class and prevents anyone else from learning, the teacher informs the principal. The principal says "Yes, sir/ma'am, I'll take care of it", removes the kid from the room, places them in a different room, and informs the kid's parents.
3. If any kid in any classroom verbally threatens or physically assaults a teacher for any reason at all, the kid is immediately expelled. Any lawsuit over this by any parent is dismissed via lack of standing to sue, and the parent pays the school's court costs.
Problem solved.
If you work at a school that can't seem to fire incompetent teachers, you'll be out of business and good riddance.
If you teach at a school, your word is SCRIPTURE when it comes to a disruptive or dangerous student. That means you have the last word about when or whether a student is returned to your class, not the pricipal or the board or some parent who can't discipline a kid.
If you're a parent and your little snowflake can't handle the concept of "don't hit the teacher and don't start screaming in class", you are free to educate him yourself.