How about not much?
There are so few school shootings and so few people killed this way that I question the need to create any large-scale proposals in order to stop the killing. I think that allowing some teachers to be armed would not be a bad thing, but ultimately, policies should not be determined by vanishingly rare events, unless they would produce a societal catastrophe (e.g. something along the lines of a major city getting destroyed by a bomb).
That is all.