All it takes is one bad teacher to ruin the armed teacher idea. I think full time LEO's in addition to the security like SMS mentioned is the best idea.
All it takes is one bad LEO to ruin the idea....
Cops kill the wrong person sometimes. That doesn't cause us to change police work much.
Cops are killed with their own weapons sometimes. We increase training to deal with that. Then again, the armed teacher is not going to be wrestling with a gunman. It'd be more like an armed pilot.........