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

Its very realistic that a teacher or some other armed individual could take down a single shooter using a handgun. School shooter and many others tend to get tunnel vision as they go about their evil. The are looking to kill and not paying very much attention to their surroundings other than looking for more targets and eventually looking for a police response. The chance that a shooter would be military trained are very slim. In many cases you could walk up behind a shooter and pop them in the head since they will be in tunnel vision mode. Even doing a mag dump at a shooter, KEEPING IN MIND COLLATERAL DAMAGE) can stop, distract or make a shooter think twice. It would help if the good guys was proficient with their weapon. The sheriff deputy that was the school resource office should have engaged the shooter and delay him at worst, killed him at best. We will never know if that man could have saved even one student because he never entered the school with his weapon which was more than the kids and teachers had as they ran, hid and suffered. Most civilians and even some military don't think about the shooter and how focused he must be and what his level of situational awareness is since he is most like riding an Adrenalin high as he focuses on the things in front of him. Anything is better than nothing in these situations.

No.

Knowledge of tactics; having a plan; rehearsing that plan; having a team and utilizing teamwork; motivation and skill. Who has more? Who put in the effort? Who can generate more combat power in a shorter time? I wouldn't bet money on one or two db's with AR-15s and a grudge against a properly prepared teacher with a handgun. On the other hand, a person with a bachelor's degree, teaching certificate and a gun locked in his desk drawer with a magazine in his pocket might not survive.

I think arming teachers is more about making a soft as a less appealing target for school shooters. there are schools that do allow their teachers to carry. I tried looking for information as to if it has been effecting - however I have not seen any news on TV about any school shooting in Texas.

https://www.caller.com/story/news/education/texas/2018/06/14/texas-school-districts-allow-teachers-staff-carry-guns-schools/670653002/

I get your question about the effectiveness of a civilian, who may only have minimal training, in engaging an armed intruder. Hold that for a moment.
Do you think an armed intruder is more, or less, likely to enter a building knowing there are multiple armed opponents he will encounter in the commission of a crime? I’d suggest removing the “Gun Free Zone” is act as a deterrent. And yes, an armed teacher would be more effective at stopping the assailant than an unarmed teacher.

Absolutely! Engagement in a school building is typically at very short range, and a pistol is easier to maneuver in a building than a rifle. If the teacher is willing to train to work in close quarters and crowded conditions, and is qualified as a good combat pistol shooter, then they can be very effective! And those who want to go the extra mile and train in fire and maneuver could do even more to take out a threat. At the very least an armed teacher could control the "fatal funnels" that exist in any school- doorways, halls, stalls, etc. That can be done with a minimum of training. We need to get away from all this hand wringing hysteria the media tries to induce. Americans have been taking care of business since we got here. I don't see why this is even a question.

The same assumptions you make for the defender (the teacher) often apply to the attacker.

Few of these creatures that like to attack schools do so in the anticipation of meeting actual armed resistance b/c the government tells EVERYONE there will none w/signs, chest thumping media releases, and repeated policy. Knowing that there is likely none, he plans accordingly.

Adding armed teachers adds to the factors such would have to think about b4 making an attack. We've seen many of these people just want publicity and not death, that's why the majority attack the unarmed, soft targets. Any wild cards that can be added into the situation might save lives, an armed teacher or twelve improves the odds of preventing such an attack or maybe mitigating it.

Moreover, if teachers want to try to defend the kids, why should we just keep saying no? Is that accomplishing anything?

If the teacher was in an open field any more than about 20 meters from the shooter, the teacher would probably be toast however, most school shootings take place indoors using a semiauto (as very few people are licensed for or have access to full auto) the teacher with some training has a better than even chance of taking down the shooter using a long gun.

Is it realistic to believe that a teacher could defend against an active shooter, using an AR-15, with their bare hands???

I rest my case.

I believe just the threat of return fire from armed teachers and staff would serve as a deterrent to most school/church shooters. Not all of course, you will always have kamikazes, but most. Or do it like we did (&still do) at the high school where I went (Benedictine Military School), an all male Catholic military school. Most of our teachers, including the priests, were combat vets. We had an armory and my homeroom was actually the rifle range! God, Guns, and Guts- Praise the Lord and pass the ammunition!