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

I'd rather a slim chance than no chance. I was in a corporate office being instructed by visiting 'workplace violence' lecturer who spent a half hour telling people how to hide and 15 minutes telling people how, as a last resort, to throw staplers, coffee mugs and telephones at an armed intruder. I'd rather put my life in the hands of a novice with a 9mm than a panic stricken victim throwing a stapler.

LCpl Mcain, you pretty much hit the nail on the head. However, most teachers would be concerned with their classrooms and students in them, not searching the halls for a shooter.
being properly trained would be a requirement in my opinion and knowing your classroom. Most only have 1 entry and exit, and no interior windows, so I would give a well trained teacher with a semi automatic handgun a very good chance. Police would still respond and the students and staff
would have a better chance to survive. My oldest daughter is a 9 year military veteran and a high school teacher...and she is an expert shot. Semper Fi Marine

KER GySgt USMC Ret.

Granted I live in the south, but I have lived all over this great nation, so my response may be colored by that: I believe that a good many teachers (coaches, mostly, but to include JROTC instructors) would be able to handle themselves as well as supporting the SRO in the course of his/her duties. Good many of my teachers growing up were either hunters or former military. And, again, growing up in the South, we teach our women how to shoot as well. No, that's not a chauvinisitc statement, but a statement of growing up in a partially chivalrous society. A good many of these teachers are also mothers, and the way I've trained women over the years to shoot as well as I can (7 times USMC expert rifle and pistol) is to put a picture of their child in the "arms" of a B-Modified type target. You'd be surprised how well motherly instinct kicks in when I do that and just how well these women shoot.

Of course you can take out someone with an AR15 with a pistol. The main advantage of a 'long' gun is range. Range is taken out of the equation inside a school. Also, you can shoot a semi-auto pistol as fast as he can shoot his AR. Does he have a power advantage? Yes. But shooting is more about mindset than the weapon. There are numerous examples of soldiers using pistols to defend themselves. Think 'We were soldiers once, and young'. The SGM killed many a VC with is .45.
One cops/soldiers opinion. But yes, you can take on an AR15 with a pistol.

There are sheep, wolves and sheepdogs...what are you?

Before I retired from teaching and after 27 years as a 12B, I believe that I could have been a deterrent if the aggressor did not enter my room first. Most school shooters haven't seemed concerned about a quick response from the next room. The issue is would I have given any consideration to the shooter to surrender? I believe the answer is no! Evil does not respect laws, so when combating evil, we can't win if we do.

Answers in this forum are going to be an echo chamber. Most of us served, a lot of us have already been in combat and have that experience of that chaos. The reality of the fact is that a regular civilian cannot be trained to reasonable standards nor maintain that standard. In most states (I say most because some states have abysmal educational systems) teachers are already spending "off hours" doing work, they also have to attend "annual training" for continued education points. Let's also not mention that psychologically teachers are in a "nurture" frame of mind. I would hate to see the mental damage done to someone that flips from "nurture" to "protector" and actually kills a student that they formerly took care of.

The simple fact of the matter is that the training does not exist. Police are a reactive force that trains on what to do once upon arriving at an active shooter scenario. The military has CQB training but that doesnt' meet the realistic issue of dozens of kids running around while trying to spot the one with a gun.

I would be more inclined to say security measures need to be implemented (like they have in NY) to deny access in the first place, but then ensure SROs are going through specialized training. Systems are already being developed to lock down key areas in a school to trap a shooter, other systems can bombard a hallway with various gasses that render anyone in that zone unconscious (including bystanders).

Long story short, no...arming teachers is not the answer.

I don't believe that the idea of arming teachers was aimed at having the teachers leaving their rooms and hunting the shooter. The intent was, to have the teachers and students hunker down in the classrooms, behind a barricade of bookcases and tables etcetera, and wait for the shooter at attempt to enter the room. Room clearing is challenging for a team of trained individuals so, I believe that a teacher with a minimal amount of training could, from an improvised barricade, successfully defend against an untrained individual intent on shooting up a school.

They are not training teachers to be soldiers. The intent is not to have team of teachers hunting down the perp.

The point is to have trained teachers with weapons around the school to do something if the opportunity presents itself, and if nothing else, provide deterrent force so that any potential active shooters will not know who is a threat and who is not. That in itself will slow them down, if nothing else.

The reason everyone shooters pick schools is for the horror effect, and because it's like shooting fish in a barrel

Look at this way...by not having any protection is a definite view of many
deaths ahead....being protected with “just a hand gun” is a major view of
waking up the next day and saying thank YOU LORD!
My saying is: “I’d rather have it (handgun) with me and not having to use it, than not having it with me and needing it.” I read that somewhere before I got my Concealed Carry Permit and it stuck with me and makes good sense to me.
So, a teacher trained, and having a handgun close by ‘will’ save the lives of some if not all of his/her students and themselves.