Tragic events in the past could’ve been less lethal if some of these common-sense steps had been common knowledge. That’s why, as sad as it seems, this kind of training is necessary and important and can end up making the difference between life and death.
Of course, all of this would also be totally unnecessary if everyone was able to freely carry. No one would bother trying to shoot up a school if they knew at least 1/2 of the people there could and would shoot back.
And have you seen most teachers? Yeah, they're going to go hand to hand with a shooter and take them out. Sure. Just another example of GRRRRLLL power trying to be realistic.