Yeah, I believe you. If only a dozen teachers had been armed.
Not even a dozen. Two or three with a good plan,willpower, and actual firearm-competence.
At Columbine, the killers knew they would face at most one armed guard. That guard was assigned to Columbine because he was incompetent with a gun. If even a handful of anonymous responsible adults at the school had carried a concealed handgun, the killers would have hesitated to even enter the school. If they had gone ahead with their plans, the loss of life likely would have been much lower. In Mississippi and Pennsylvania, school shootings were stopped when armed adults intervened several minutes before police arrived
http://www.rmgo.org/alerts/2001-sb83.html