You don't.
Contrary to the nearly unanimous opinion of legislators, more legislation is usually not the solution to a problem. In this case, the solution is to defend helpless, innocent children against predatory monsters. Legislation means precisely nothing to a deranged, suicidal murderer. The only possible value of piling on more laws is its analgesic effect for the class of politicians and their constituents who have long since lost touch with the real world.
Our school children don't need more laws to tell them that the guy shooting them in the head is really, really, REALLY bad. Those laws have already been written; they didn't help. The innocent victims of such bloodthirsty demons need someone to protect them. They need someone who can and will kill that monster rather than let him get to them.
Arm teachers and school administrators.