Is it realistic to believe that a teacher could effectively defend against an active shooter, using an AR-15, armed with only a handgun?

Shot placement is the key. Granted, if a bad guy is armed with a rifle as opposed to a handgun, he may have an advantage in quantity of ammo and sight radius; but the key is "ordnance on target". I'd rather face a rifleman with a pistol than a yardstick! Also the "On scene" police officer in Florida did not attempt to confront the shooter! Apparently he was a member of the "ROAD" gang!

I think perhaps. Remember the shooter is firing at random, not taking any thought on aiming; just spraying bullets willy nilly. A teacher who has been trained properly could take a head shot from behind or to the side. This takes any flak jacket out of the picture. Perhaps the odds are not that great, but worth a try.

No and they shouldn't have to. They do not even get paid enough to do the job they do now and people want them to be armed security, its ridicoulous. If your going to hire security then hire security, not to mention people who will actually confront the shooter unlike in florida.

I think you are making a lot of incorrect assumptions. The teachers are to protect their students, not seek out and close with the enemy. They are on defense not offense, when the shooter enters their sphere of influence they engage. The distance is short and they have the advantage.

In the response plans I've seen, none have them had the teachers go on offense and close with the shooter.

I suggest that you consider the psychological profiles of these "active shooters" before doing any further commenting. These "active shooters" are not very proficient with weapons and their motives are not to kill or wound but to spread terror. They also want to control the situation and, if that control is threatened, they suicide. So, the mere presence of a teacher with a gun should be enough to make the "active shooter" suicide.

One of the common denominators of these mass shootings is that they happen in "Gun Free" zones. The thought, by the shooter, that someone "might" shoot back is usually a deterrent. Growing up in Oregon, guns were a daily part of life, kids brought them to school to work on in shop or to show off to friends and go hunting after school. Should teachers be armed? Hard to say really, the better question is why should they have to be armed? Too many "victims" in this world, not enough responsibility for our own actions.

Most active killer events happened in 'Gun Free Zones'. A predator chooses these areas because he does not expect resistance. Just the impression that he will be met with force is usually enough for him to change his mind (This happened in the Charleston SC church shooting). Bad guys like this usually do not have plan 'B', they just move on to an alternate target. Hardening these soft targets is the only sure way of protection. Legislation and politics have to be secondary to this. I believe that training willing teachers and hiring veterans is the key. People intent on a body count will choose the path of least resistance.

Ladies and Gentleman,
As a combat veteran with tours in Iraq, and a 4 month stay in Northern Africa I would have to say no. However since I exited service and started work in the private sector as armed security I can say that I have seen a great many capable folks with very little experience and some training become very effective in protecting property and people. The key is mindset. Why are they doing what they are doing? They want to the feel it is their duty to preserve life. If any person is driven by a belief they can achieve this aim.

"Is that realistic?" My first response is no for many of the reasons you have stated. Being realistic of course, communications and fast-moving mass shooters make co-ordinated response nearly impossible on the street. Schools are different in that they are enclosed and could be monitored using technology for sound, audio, and live video feeds of moving threats. Computers are in every classroom. Using audio monitors, a scream or a gunshot can trigger a computer network to override all open applications in the classrooms and display an emergency screen presenting all the tactical details of the event to every computer in the building. Real-time monitors in classrooms give teachers informed options if they follow the first rule of a gunfight. That is to have a gun. Training and technology are much faster than 911 and the Police who will remain outdoors until help arrives. The same emergency network in the building can also be broadcast outside the building via wi-fi or dedicated police radio data networks providing for a much more rapid tactical response. Think of the possibilities using computer algorithms tied into this emergency network to broadcast and misdirect the intruder opening chances for coordinated responses and concentration of firepower, etc. "Realistic?" In today's world, everything seems unrealistic and surreal. We have been dealt this hand of cards and we have choices as to how we play them. An active shooter has called your bluff when he gets inside to start with. You must use every trick up your sleeve to win. We have the "Technology" and "Economy of Scale" given the number of schools in America would make it a bargain against one child's life. Think of the many 10's or 100's that could be saved over time. That seems like a realistic option that I have not seen on the table.

I think you are very misguided marine. You also fail to mention the million + lives saved ever year by ordinary armed citizens. A teacher with a gun is 10,000% better then a teacher without a gun. You said it yourself, police officers have a hard time with the "fog of war". But like millions of people every year who end up protecting their families, loved ones and themselves with a firearm, not all are successful so your right to a point. That point is, there is nothing that is 100% certain. But give the kids in school a better chance by having more good guys with a gun. Instead of just waiting for help to arrive minutes to late.... Which by the way are good guys with a gun!