You expect a 60/50/40/30 year old teacher to have the composure to open (unlock) a drawer, get the gun out and hit a target with screaming, crying, children and blood, brains, arms and legs flying all over the place? With the right training they would be better prepared to deal with it. Training is essential otherwise your scenario would be true.
If you've been in the military then you've been trained to kill and I bet you couldn't do it either.
I've been in the military, was taught to kill, and must have been successful at it because I'm still here. I would not hesitate to stop a killing if armed.
Hope this helps
..............al
What part of "shall not be infringed" is unclear?