You know you were thinking it.
On a more serious note, I don't think that giving teachers guns is the way to go, as they would have to be taught how to shoot them, and personally, I can't imagine a 1st grade teacher, who, like mine was, is 80 years old, and is half senile, shooting someone.
However, my 12th grade world history teacher was a marine, and could easily take out some punk kid with a shotgun from 50 yards. Honestly though, even if you gave all these teachers guns,it wouldn't prevent much, it might even increase the risk over time, especially if the teacher sprays and prays.
I think prevention, and identification of the youths that are at risk is the most important thing. A child could always bring in a machete or a sword instead of a gun, or, an explosive, and still injure or kill a lot of people. Teachers can't be everywhere at once.
It's a tough problem, it really is, however, gun control is obviously not the way to deal with this.