I'm not going to pretend to have an answer to this cultural problem, but I did want to comment on the reaction of "let's arm the teachers". Overall, I am pretty strongly against this idea. Here is my take:
1. It could be a deterrent.
2. It could limit casualties.
3. Relatively cheap and easy implementation.
1. It could be a deterrent, but that's about it.
2. It could limit casualties, but barring highly idealized situations, won't actually stop these shootings--making it a bit of a half-assed "solution".
3. Relatively cheap and easy implementation--if you get full buy-in, which is extremely unlikely; it would pretty much require every teacher to be armed to be remotely effective in stopping these shootings.
To expand on the cons a bit (since I'm trying to show why I do NOT support this idea):
Realistically, it most likely won't actually stop a shooting, it can only hope to limit the casualties. Even if the teacher is armed, a rampaging student will most likely get off several shots before an inexperienced (in firearms & self-defense) teacher could draw the gun. Further, if said shooter(s) think the teacher has a gun, that may just make said teacher the first target; again, without extensive training, they'd be down before they could do anything (see video above).
While the theory is sound--armed citizens keep people safe--the reality is that it doesn't seem to hold much water. This is another solution that requires several ideal assumptions to be true--every time. (e.g., the shooter has to come into a room where the teacher is armed, the teacher has to react faster than the shooter...otherwise, it won't stop the shooting, it will at best minimize casualties). And how much of a deterrent will the possibility of getting killed be when
many of these massacres end with the shooter killing themself?
How many teachers would want to carry a gun? I like guns--grew up shooting them--which probably (I have no data to back this up; just an assumption) makes me unusual as far as teachers go. However, I would never take one onto a campus--way too much liability for something to go wrong, for starters. (God help the first teacher that, for whatever reason, has their weapon accidentally discharge on campus, regardless if anyone is hit.) But most importantly--have you seen kids these days? Half of my male students--and a handful of female students--could easily overpower me and take the gun with little problem. Between that and the potential for accidents, this situation has "mistake" written all over it.
The last one is more of a cultural awareness. When you think of a place where teachers have to be armed to keep kids safe, what/where do you think of? I think of stereotypical third-world places. Is this really what America has come to? As the president said, surely we can do better than this.