It seems that most of the recent mass murderers have sought out "gun-free zones" in which to kill their victims. The Aurora, CO, shooter, as I understand it, drove past a theater that allowed its patrons to carry guns and carried out his plot in a "gun-free zone," where I'm sure he felt more certain he would not be stopped by an armed audience member.
The school children are already in the care and protection of school administrators and teachers. If those people cannot be trusted to carry concealed weapons, then maybe we really do have a much bigger problem than mere crazed shooters from outside the school! I'm in favor of allowing law-abiding people to carry their weapons, wherever, though I would hope they would be trained in the use of the guns.