Mac you can only think of two possible ways for teachers to act. Running thru the hallway like clowns, or hiding under the deck. You make the hallways sound like a maze of curves, deadends and blind corners. Every school or college I have ever been in has straight hallways. Shooting range straight if you know what I mean.
If you can't understand how a person could stand themself in danger, then leave it to us that will.
You are correct that the first and best way is to stop them before they can get into the school, but the Anti's shout that option down just as hard as arming teachers, or having armed guards at the school.
They seem to think guns have a gravitational effect on other guns and pull them all together.