What size and type of weapon would be easy to hide and be effective against a high powered semi-automatic rifle in the hands of a crazy man wearing an armored vest?
Who is going to pay for the initial and refresher training for the armed 5’1’’ first-grade teacher?
Is a so-called gun-free school zone really an open invitation to a messed up kid or young adult bent on shooting up the place? If a shooter intends to die either by cop or by self, an armed zone would seem to have little deterrent value.
Dylan Klebold had a long history of suicidal thoughts, and he killed himself at Columbine. Seung Hui Cho, the Virginia Tech shooter, also killed himself. Jeffrey Weise had a suicide attempt prior to his attack, and killed himself during the attack. Lanza the Newton mass killer killed himself, the Cleveland school shooter also killed himself.
In my opinion a hardened single-entry building with a CCTV would be more effective than arming amateurs that could cause more harm than good in the confusion of an attack.