Make it mandatory for a certain percentage of school to staff to be armed.

There needs to be a law that makes it mandatory for a certain percentage of a school staff to be armed. School shootings are too common for comfort and there rarely is a police officer even near the school. If teachers are trained and aloud to carry arms, it would first detour anyone from considering a school shooting, and in the case where a shooter is present, casualties can be kept minimal because the teachers would be the first line of defense.
More gun control simply won't work, there are far too many guns that almost anyone can acquire. And the shooters obviously aren't obeying the "gun free zone" signs, so lets put a first line of defense in order.