Schools are already gun free zones though?!?!
Look, I truly get where you are coming from but a single armed guard (which will be the best case scenario due to budget constraints) will simply be the first guy a batshit crazy asshole like this shoots.
Seeing as this is an elementary school, I am not exactly sure what the answer is. Most of the adults are women and women tend to conceal carry in their purses which are often out of their direct control while they do their jobs. I highly doubt that I would bring a gun, regardless of legality, into a situation like that. With that said, I think that empowering the people that will actually be there when the shit hits the fan to put an early end to the situation is the absolute best we can do. I simply don't have another answer for a situation as horrible as this and regardless of what some people think banning a few items won't do the trick.