Do you hate children so much that instead of trying to think of a real solution you'd much rather just gamble with their lives? I mean, I'm not the biggest fan of other people's kids either, but risking their lives just because you're playing party politics? Shame, really. For one, your link on the statistics of armed civilians vs unarmed? It doesn't take into account that those armed ones were luckily there in the first place, so for "your" solution to work would require a Greg Jenko in every class room, not just one at some random place of a large facility. Something you keep ignoring, by the way. So in reality, the chances are just as good that by the time the designated Morton Schmidt found out about the gunner, ran to where the weapon was stored, got it out of the locked room, prepped it, and ran back there could be the same amount of dead kids.
Are we really so afraid of guns that we'll ignore this possibility?
That doesn't even take into account that now he's possibly out of breath and on an adrenaline high or the lack of training to deal with the situation properly, but there's already enough variables to blow up your hole-laden Death Star of a hypothetical without tossing in some ewoks.