Haha, issue teachers Dragon Skin vests (they are real) and riot shields. Maybe stun guns, tazers and batons too. Guns are too lethal, and too easy to kill someone with.
The problem with guns is that not a single person in this world is trustworthy, even teachers have feelings, and that includes anger/rage. It isn't a judge of character deciding who gets a gun imo, it is a judge of how much restraint they have. (It is not easy to test restraint with any accuracy)