Create a "Federal School Marshall" program like we have on domestic airlines to protect schools.

Implement a rotating Federal Marshall force in schools posing as staff, just like they pretend to be an airline passenger, and if something comes up, there could be a response to an attacker. Every school doesn't need one every day, but the idea of someone fighting back should make an effective deterrent. and maybe the "threat" would have second thoughts about attacking unarmed children/staff.