Federal law says you can't have guns on school grounds unless the school and state work some law/agreement, whatever. Some states have passed their own laws prohibiting guns on school grounds, but for those that haven't this is an immediate option.
I'll tell you want I find most heartening and in really doesn't have anything to do with the guns. It's the fact that the school themselves are taking action, on their own, they are doing something. Beats the hell out of crying to the state and the feds to do something for them. This is a positive thing. Imagine this, people trusting their school staff to be responsible, who'da thunk it?