However armed security at schools isn't the answer.
1) If you think about the school shooting at Virginia Tech that killed 30+ people, its a little known fact that SWAT was roaming the campus prior to the shooting and were less than 5 mins away from the guy. He still killed 30 people within fairly close quarters. Or look at the Las Vegas shooting as well. Or the recent shootings at military bases. Again security was there and it meant basically nothing.
2) Even if the numbers of armed guards are so high that it truly is a deterrent to these types of shooting, these crazies will just find softer targets like malls, churches, events, etc You can't have soldiers everywhere.