(The first (brief) part of this post expands on what I said in my comment. The 2nd part suggests prevention-measures.)
I was badly bullied in middle school, from 1957 to 1959. 7th and 8th grades. At that time, middle school was called junior-high school. I'm 70 years old now.
I was regularly, daily, threatened, battered, and assaulted because I was quiet, non-aggressive, and didn't join any groups.
Obviously, if anyone, including a juvenile, committed those crimes against a teacher or school-administrator, he'd be jailed. But no one cared if those things were done to a child.
I can say from experience that continual violent bullying can contribute a lot toward destroying its victim's life.
I was bullied in high-school too, but violent bullying was worse, and more damaging, in junior-high school.
I signed the petition about Upstander as a word. But words won't stop bullies. Force is the only language that violent bullies understand.
Here are some suggestions to stop violent bullying:
I suggest some stronger anti-bullying measures:
1. Enforce the Law:
The laws against battery and assault aren't written with exceptions. As written, they apply to protect children too.
But they aren't enforced in schools, unless an adult is the victim. If a juvenile attacked or threatened an adult (teacher or administrator), the crime would be prosecuted. But if the victim is a student, a child, then the laws against battery and assault aren't enforced.
Those laws must be enforced unformly. Even children should be protected from battery, and from assault (which is defined an immediate threat), even if actual battery doens't occur).
Battery and assault are illegal on schoolgrounds, even if the victim is a child. Enforce it.
The penalty for threatening, assaulting or battering a child on a schoolground should be no less than the penalty for threatening, assaulting or battering an adult on the sidewalk.
...Some years of prison-time.
...regarless of the age of the perp.
2. No Compulsory Victimization:
Forcing a child to attend a school where s/he is being assaulted, or bullied in any way, can't be justified. No child should have to attend a school where such conditions exist.
If there are no safe schools in the area, then home-schooling, individual teacherless study, should be allowed and materially provided-for. ...&/or maybe transportation to a more distant safe school.
3. Separate Schools for Threateners, Assaulters, and Batterers:
People who have committed those crimes have no right to subsequently attend a school for non-assaultive students.
Maybe there could be special violent-student schools. Or maybe the violent juveniles should just be permanently expelled from school.
4. School Policing:
The cost of having 1 or more police on-campus is negligible compared to the cost of bulling, to its victims. Police patrol the streets to enforce the law. Why shouldn't they be at schools too, where they're certainly needed. (But they shouldn't waste their paid time on victimless crimes).
The cost would be a tiny percentage of the cost of operating a school, with its many teachers, custodians and administrators.
There should be both plain-clothes and uniformed police.
Instructors and all school personnel should be required (on penalty of dismissal or prosecution) to report threats and violence, which should always be prosecuted.
In these ways, violent bullying could easily be stopped.
If these measures sound harsh, then try the experience of being threatened, battered and assaulted at school.