If just one teacher had been armed, this could have been dealt with.
All the guns belonged to his mother/teacher.
Yep.
It's so easy to hide a little .32 Seecamp, or an S&W Ladysmith, in your pocket. Plus, there are holsters that can hide larger handguns under a suit jacket or even the small of the back.
Ideally, a couple of designated and properly trained teachers could simply open carry in the classroom. It would likely be a distraction at first, but the kids would get used to it and forget the gun is there after a couple of weeks. Once the initial... um, ...weirdness... of a couple of veteran teachers open-carrying sidearms became the norm at the school, can you imagine how much better the parents would feel about the safety of their children? The entire staff would also end up feeling an extra sense of relief.