You know, I've done quite a bit of thinking about this, and have spent a great deal of talking with my roomie, and here's the solution we came up with.
Arm ALL teachers with either police grade tasers capable of shooting accurately up to 35 ft, as well as can fire up to 4 darts before needing to be reloaded, or, with an interesting little paintball gun that I saw on a documentary a few weeks back. The paintball gun is CO2 powered, and the paintballs are filled with mace. They also can fire up to 100 ft. accurately.
Why do I suggest these measures instead of a gun? Because I don't know if the teachers are going to be able to handle the responsibility. There have been many stories over the past few years where teachers have accidentally shot themselves in school with their guns.
And, there is the fact that most of these school shooters are counting on being killed. If a teacher has a gun, then the shooter has probably a 90 percent chance of being killed and not able to stand trial. If they are taken down with mace balls and tasers? They won't be killed, and can also be held to account for their actions.
Would also be a lot safer for all involved. I mean, which school are you going to attack, one where maybe 2 or 3 teachers might be armed, but you might still have a good chance to kill a bunch of people before they get to that area of the school, or a school where EVERY teacher is armed with a taser or mace gun?