We are speaking at each other, but not conversing. Heroic acts can be accomplished under these circumstances, and have been, as you mentioned. But most, if not all of these acts involve fleeing, hiding, shielding i.e., the flight part of "fight or flight." That is my point. This is what differentiates the two widely disparate groups of trained people we are talking about: teachers vs. trained military or law enforcement personnel. Each has a very different instinctual and/or trained "fight or flight" response, simply based on their chosen profession and daily life/culture/job.
I agree that a shooter knowing there are armed persons around may be a deterrent, but that did not appear to phase the Va Tech guy on a college campus with known campus and/or local police we all have seen on campuses. But maybe he knew where he could get away with it for a given period of time before police responded.
I agree with a fully trained police officer assigned to a school, not just a rent-a-cop, but someone who engages in regularly certified training under these tactical circumstances.
The original point was not to arm teachers as a deterrent though, it was to arm teachers to put a bead on a killer as he is shooting up their room. That to me is far from realistic, as I have argued.
Finally, this isn't lunch room duty training, or brushing up on CPR certification for a potential recess accident. And it doesn't matter whether or not the wacko shooter is trained, because he is actively shooting a weapon at you and your kids in a limited space classroom. He has the advantage of surprise, offensive action, and he is committed mentally and psychologically in the moment. The teacher was just correcting a quiz, or erasing the board, and now must act in a 180 degree shift of everyday reality in an instant, accurately with a weapon he or she has trained on sporadically in is or her spare time. It's just not realistic for elected officials to even propose this. Deterrent maybe - but better to use a trained police officer at the front desk; realistic counter-offensive or defensive measure - not realistic proposal.