our federal budget doesn't even allow for the teachers to arm themselves with enough pencils to the last the entire school year, there's no feasible way we'd be able to afford arming teachers with a gun and the proper training to go along with it. Then there's issues like a student overpowering a teacher or a teacher being accidentally mistaken for the shooter by a trigger happy cop in the heat of the moment, or a cop getting shot by a panicking teacher,. Plus I don't think it would create a safe and friendly learning environment for the students.
While I do agree that arming teachers could theoretically fix the issue it's just too shortsighted to be feasible.