Acknowledging that turning the screws tighter to obtain "compliance" causes people to suffer mental issues from "zero tolerance" based policies goes against the theory that increased authoritarianism is a valid solution, and that is not something that authoritarians want to hear.
You see, children "acting out" (eg, refusing to conform to the imposed 'order', et al) is not considered symptomatic of an underlying failure of that system or the 'order' it seeks to impose; (Like it SHOULD be)-- but instead as "The dreaded thing" that must be stamped out viciously. Never mind that petty authoritarians are attracted like flies to shit to small (and therefor, seemingly meaningless) positions of authority, where they can rule their imaginary kingdoms. (See for instance, the local serial killer from my area, Dennis Raider, AKA-- "B.T.K."--- Guy attempted to be a police officer, but could not make the cut, due to his petty authoritarianism being so pronounced; instead gravitated to being a church official, and a dog catcher-- positions he used to torment other people to satisfy his authoritarian streak. His inability to climb to higher positions of power were partly the fuel for his homocides; He had a deeply seated need to feel superior to other people-- to be "In control", "In charge".) Do I think *ALL* school systems have these kinds of people running them? What-- are you stupid or something? No-- But enough of them are in that system that there are *REAL* problems in it, and groups like the teachers unions dont help matters any in this respect.
To solve the problems with school violence in the US, a very radical change to the WAY schools handle and approach violence must be taken. Specifically, that zero tolerance shit needs to be deep six'd with prejudice, There need to be psych evals of school administrators and teachers at regular intervals, and above all-- god damn it, when a student withdraws from their peers, becomes insular and isolated--- FUCKING ACT ON IT, INSTEAD OF IGNORING IT. Yes-- Even if that means suspending the popular girls, and the rich kids (should they be involved in causing the problem.)
Other things that can greatly improve the situation:
Allow parents a better set of options to send their child to a different district in cases of mental health breakdown from toxic peer environments. Just because it is logistically "difficult" to enable that, does not justify making kids into killers for the convenience of politicians. If a child needs to change venues, CHANGE THE DAMN VENUE, AND DONT COMPLAIN. (And yes, if that exposes your school as a place where children are routinely victimized, guess what bitches? ENJOY THE INVESTIGATION! There is a difference between "Low income" and "Likely to cause lasting mental harm to children". One can be the former, and NOT be the latter. Enabling children to have a legitimate means of escaping an abusive environment, where currently they are forced to endure in some twisted fuck's private little hell for them due to quirks in the legal system, would go a LONG way toward alleviating this kind of extreme response, since it allows the problem to be sorted before it reaches critical levels like that. Lame excuses about how "parents would seek out counselors to declare their child mentally harmed by low income school systems en-mass" are histrionic bullshit, and I wont accept that line of argument without some actual data.)
Stop allowing the teacher unions to protect harmful teachers (via the psych eval process, to clinically evaluate teacher mental health, and should they be found unfit, provide appropriate mental health services for the teachers. Naturally this will require a completely neutral evaluation service. Ideally with a random rotation.), because
"Compassion fatigue" is totally a thing, and teachers are NOT immune. This is not the same thing as demanding the dissolution of teacher's unions-- (they are a necessary evil)-- but they cannot be unchecked either, because that is how you have pedophile teachers that stay in the system for decades, due to the insane paperwork that must be done to fire a teacher. This is ESPECIALLY true with the absurd classload burdens imposed on US teachers.
Which brings us to--
Smaller class sizes, more, smaller school buildings, more spread out. At the worst, this will mitigate the number of casualties because there will be fewer students to be shot by single crazed students. Impose actually sane limits on the size a school building can be, and tell cities to suck it up buttercup, and provide appropriate zoning or lose federal funding.
I have other remedial suggestions, but they are equally unpalatable politically.