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

If the schools had trained teachers and service personnel then just maybe these idiots would think twice before trying to shoot up a school because they will not know who is armed and who is not. Just the thought that this area IS NOT A GUN FREE zone I believe will make some not to attempt to try and shoot and try to cause harm

Yes, they can. People are learning to fight back. Did you see the most recent incident where a single individual took down the shooter with the AR without using any weapon? Training that focuses on key factors is important no matter how minimal it is. Concentrating exclusively on the mechanics of using a weapon is a mistake - an individual can pick that up on their own with time and location to practice. More focus needs to be on preparing yourself for action. You are right that initially EVERYONE has a primal reaction to an attack. If you are in the immediate vicinity of the shooter, don't bother with your weapon during this stage, just scream and attack. If not, use this stage to find cover for a few seconds to collect and calm yourself, draw your weapon, assess the situation (e.g., am I within range), put your brain in combat mode, and take careful aim. Forcing the shooter to take cover can be as good as hitting them if it saves lives and buys time for others to escape or join the fight. A teacher firing into the ceiling might be just as good as firing at the intruder - shifting them into fumble-mode. Every weapon has to be reloaded.

A real question that swe really don't know the answer to at this time. However, there is an ancillary question: Does arming teachers, and thus increasing the number of guns in society the answer? Since we have lots of shootings that occur without any "visible" mental illness, how do we screen teachers? I am not a teachers, but have in-laws who are, and they tell me about teachers in their schools who are very stressed out for lots of reasons, and kids push them pretty hard. That's not a good situation to put guns into play. Teachers, then church goers, then firefighters, then bus drivers, then... Look at other countries. We have a gun problem that can't be solved by more guns. Period.

If you and I can be properly trained to handle a firearm, if millions of PD officers who did not militarily serve can be trained, if even more millions of American citizens can be trained to properly carry and use firearms, then I see NO reason a teacher can't be.

There are good people that end up defending themselves, others and their homes EVERY SINGLE DAY with a firearm AND who are forced to shoot someone in that process... And guess what? They do it even though they have NO experience at all with combat or police work..

So why would you think it any different for a teacher? It is not. And for teachers to carry IN a school, they are required to get actual training before they are allowed to do so.. MUCH more than your standard every day home owner or CCW civilian.

The answer to that question is very situationally variable..a fancy way of saying "It depends.."
I would ordinarily always want a long gun to fight someone who is also armed with a long gun. But if you are in confined terrain or inside a building with many rooms, hallways, closets, etc., then sometimes a pistol is a more flexible choice. A semi-auto pistol with a good sized magazine or a bull-pup model shotgun with a shorter barrel than the normal shotgun would seem a good choice. Now, could a teacher use a handgun to defend a classroom against an active shooter armed with a long gun? Maybe, but there are many factors to consider. Does the teacher have any warning? Can the teacher or students lock their classroom door to impede or delay the shooter's entry? Does the classroom have a door with a window and locking mechanisms that can withstand gunfire? And perhaps most important, does the teacher have sufficient skill and determination? Does he or she go to the range to maintain shooting skills? Many teachers I've met are politically progressive/liberal and don't want anything to do with guns, in fact many of them want to take guns away from ordinary people. I'd suggest hiring armed forces veterans with marksmanship skills and good background checks to supplement security at schools rather than trying to arm teachers, most of whom have no firearms training and many of whom don't believe in using firearms for self defense.

Said it for many years, probably elsewhere in this forum. Arming teachers isn't the answer. There are thousands of Iraq/Afghan vets out there, highly trained, still young and in good physical shape. I'll wager these people would jump at the chance to protect our students. Of course the vetting process would have to be stringent, but IMHO, that would be a better, more effective deterrent. A helluva lot more than "No Gun Zone" signs. Let teachers teach. Leave security to those who know how.

I am tired of the comments that equate teachers having a gun with issuing a gun to any and all teachers. This is a dishonest attempt to make us believe we will simply issue a gun to all teachers - whether they want one or have any idea what to do with it.

Of course it is realistic to expect a trained and determined teacher to make a difference. Shot placement counts. It is impossible to dispute that a trained teacher with a gun wouldn't have made a difference in almost every mass school shooting. A hit with a handgun trumps a miss with a rifle...every time.

Not without intensive training. I wouldn't even trust veterans to be able to neutralize a shooter in a classroom full of kids without accidentally hitting one unless they had intensive training and regular refresher courses.

So what's the alternative? If a teacher volunteers to be armed how are the odd any worse? An armed teacher is more of a deterrent than an unarmed teacher (though politically less useful than an unarmed teacher who died shielding her students). So do you want useful corpses or resourceful armed teachers.

They are the first respond, they do what they can to protect our children. I say give them a weapon so they dont have to shield our kids with just there bodies.