Don’t they have books? Can be very heavy, readily available - maybe they don’t act as a projectile so well because of the shape, but still. And then there’s chairs and other things. Why do you need to bring in additional items to use as weaponry?
Though I find it very sad that such things even need to be considered. Something needs to be done about the mental health care. I was once a bullied kid, and I once wished for revenge on a particular schoolmate (not death, just a little stab), but that luckily passed. For some, the anger only grows.
Hmmm. Throwing heavy pieces of metal at a bad guy to stop them. It seems that there should be a way to automate this – perhaps using some type of flammable, granulated, solid propellant to drive the metal. I feel an idea coming on!
Aside from being so low probability that those canned goods are wasted(and, in any case, why cans? Are rocks not good enough?); the “Throw stuff at gunmen” strategy is strictly second rate as strategies go.
If your back is (literally or proverbially) against the wall, and you can’t do anything else, the situation is dire enough that hoping for a lucky hit with some sort of improvised projectile doesn’t hurt; but if you do have better options(like ‘running’ ‘hiding’, ‘attempting to put locked doors between yourself and the shooter’, etc.) feebly throwing things just increases the duration of relatively close range exposure to gunfire, which is notably bad for your health.
Especially given the force that a middle schooler can put behind a throw, and the (lousy) accuracy of terrified and largely unpracticed throwers, throwing things might actually be less effective than attempting to rush to melee range. You won’t necessarily make it; but if you do the degree of disparity in equipment is going to be lower. Guns are exquisitely efficient mechanisms for putting projectiles into targets, hard enough to do damage. Throwing cans? Maybe if you have a group of the school’s best pitchers concealed at medium range; but that’s a best case scenario.
See if you can keep at least a few glass-platter era ones already opened and ready to go: I can tell you from unpleasant experience that, if cracked, a glass platter forms an edge sharper than a razor. Passes through soft tissue so smoothly that you don’t even know you’ve been cut until you start bleeding all over the place.
Just like the edges of a cheap desktop PC case. Back in my PC building days, I left more DNA (get your mind out of the gutter!) than I would care to admit inside of just about every PC that I built for somebody.