Schools are afraid to punish bullies if they are:
a) Brown
b) Special Ed.
c) LGBT-Q
d) the children of litigious parents
e) the children of parents of means who might become litigious if their bullying child is punished.
That means that a large percentage of bullies are immune from consequences.
By the same token, defending oneself against a bully, instead of tattling on the bully (to school officials who will do nothing), is punishable with no distinction between the bully and the bullied.
Combine that with the high-pressure standardized testing, constant refrains of woke propaganda, and the social pressures that teenagers have always had since time immemorial, and you have set up ideal conditions for such events.
And yes . . . the fact that government doesn't own all the guns in this country and we have the second amendment means that such events will be more deadly than knife attacks, molotov cocktail attacks, etc. Deal with that with secure entrances, metal detectors, and armed security, the same way we deal with that fact of life in courts, congress, the whitehouse and city hall, not to mention many civilian companies.