The answer is more armed security within the schools. Criminals don't abide by gun control laws anyway. In addition, limiting magazine capacity on weapons won't work either because a nut case, goofy enough to shoot children within a school, will only carry in more magazines along with their weapon(s).
The answer is, even though we don't as a society want to admit it, is we will eventually have to post armed security guards within all the schools to ensure the safety of the children in the building.
It's discouraging to know that we'll have to do this, but that's what our society has succumbed to.