This is retarded. Why are we supposed to assume that the type of shitbag who wants to murder school children only wants to do so with an AR-15? The Columbine fruitcakes built pipe bombs. It's not hard to think of a method or two that would likely defeat these bullet-proof shelters. Is it really a good idea to gather so many people up into one tiny confined space?
In this age of increasing decentralization, is it really necessary to gather 500 children together in one facility every goddamn day?