Arm principals with shotguns, rubber shot
Perhaps schools should have a gun safe only accessible by the principal or vice-principal, that has a 12 gauge pump shotgun loaded with rubber shot - the kind used for crowd control. It's generally non-lethal, but will still knock the hell out of some assailant. But if you miss, you are far less likely to kill an innocent bystander.
If the bystander in Oregon who did have a concealed weapon had rubber bullets, perhaps he would have tried to stop the maniac. I understand the hesitation in our sue happy society. If you take a shot at the nutcase who is shooting everyone and you get him, but also bring down an innocent, you'll probably be arrested for voluntary manslaughter and sued by the innocent.
The morality of the day is "protect your own ass; every man for himself." But since schools are government run, all kinds of legal protection are available stemming from sovereign immunity. Train those administrators in the ways of Rambo. Hell, if Rambo was the principal, kids would do more work anyway. Maybe that's the answer - only hire principals who are ex-special forces. And play the Green Beret song every morning over the loudspeaker.
Torin K. Andrews