Had there been an armed teacher or other school employee there likely would have been much less bloodshed and a much quicker resolution to the problem. Depending on the source American citizens use firearms to stop crimes from 500,000 to 2,000,000 times per year.
And in case you hadn't noticed, with the exception of Gabrielle Giffords, virtually ALL of the mass high body-count mass shootings happen in "GUN FREE ZONES". Just how safe are those "gun free" zones do ya think?
You know how "GUN FREE ZONE" translates to someone like school shooters? TARGET PRACTICE!! It screams TARGET RICH ENVIRONMENT WITH LITTLE TO NO THREAT! Add in the threat of armed response and you get reduces chance of this type of event.