School security is a Catch-22 situation; either the school hires armed security guards and puts one in each classroom, or they arm trained and qualified teachers. That is IF they want to prevent anymore Columbines.
Those of you citing examples of demented teachers wielding firearms in the school seem to have no problem with arming the police....some of which have been severely demented themselves.
By the way, I read an official summary of the Columbine shootings that was issued some months after the shootings, and the conventional wisdom that was first quoted about Harris and Kliebold being picked on outcasts was bunk. The little salamanders were just that...salamanders. The leader, Harris, was adjudged to be psychotic and violently anti-social. For no reason, apparently, other than he wanted to hurt people and break things.