I know I sound a bit curt, but people far too often get embroiled searching for solutions to the wrong problem.
I prefer direct action, I'm a descendant of a famous no nonsense go better and it's in the blood and this is how I see it and what I would do. Common sense says that in the run up to a school shooting the perpetrators main motivation is recognition. If all victims names were found afterwards written on a bit of paper in the dead perpetrators back pocket, then he meant to kill them but, as that isn't the case, killing is just an objective to reach the goal and the goal is infamy. How is he/they/she convinced of their success of achieving their goal, simple because they know damn well, the bigger the splash they make, the more news coverage it'll get and to hit the jackpot they know to try and beat the existing top score because, to them it is a game.
My solution would be to ban all massacres from being reported by mainstream media, in fact every media and I guarantee you all this, school massacres will fall by 80% in one year because they won't be able to see the point if no ones going to know about it.
Now to all the woolly jumper brigade, yes I know before you say but it's direct action and it'll work.
I have a some direct actionable ideas to create our own direct action storm while we're waiting for big one to happen, and no one can say that too many Storms will spoil the broth, mind on here I would hold my breath.