I’m quite pro-gun, but I think asking teachers to carry guns in their classrooms is a bad idea: it isn’t obvious that a teacher would know what to do with a gun or do it effectively; a school with armed teachers might be an even more appealing target for a school shooter; arming teachers carries its own cloud of practical and ethical problems.
Allowing teachers who already have CCW licenses to carry at school is a less extreme version of this idea that should be tried in a limited way, though I personally don’t have high hopes for it either.
There is a strong urge to “do something” after every school shooting. This is a good thing, provided 1) we have good reasons for what we’re doing, 2) we know all the reasonable options we could be pursuing but aren’t, and 3) we know why we aren’t pursuing them. However, I don’t think these provisions have been met by nearly any proposal that followed a mass shooting crisis.