Wouldn't an armed defense be the last resort? After all, if the shooter is in the building, that poses the maximal risk to students and teachers. I can think of a number of steps off the top of my head that a K-12 school could take to protect itself that would come first.
1. Secure, bullet proof entrances controlled from the inside, with cameras.
2. A double secure entry vestibule with a metal detector.
That's just going to create a queue of targets outside of your hardened area.
3. Hotline to nearby police station.
4. Secure classroom locks.
And so on. The priorities should be preventing an armed assailant from entering the building and then securing classrooms inside the building if an assailant gains entry. If you have to prioritize resources, those listed above I suspect would provide the best bang for the buck (sorry for the pun). Hunker down and wait for the police to arrive.
I wrote this over six years ago:
My suggestion to reduce mass shootings like active shooter and domestic violence looks at three actions: prevention, isolation, intervention.
Prevention is the process to reduce the chance that a shooter will have a firearm in the first place. It's easier for DV than for active shooters, as the Lautenberg Amendment can be used to disarm anyone convicted of domestic violence or with a personal protective order sworn against them preemptively or actively. For Lautenberg to be effective, we need to educate potential victims, their legal support and local law enforcement. Potential active shooters don't have that history and with HIPAA restrictions find it easier to pass background checks. Prevention against rampage shooters is much less effective.
Isolation is the action of keeping a shooter separated from his victims. For DV, removal of the family to a safe house is the primary tool, unless the DV offender commits another crime or is caught violating a PPO before any homicide attempts occur, when he can be arrested. For active shooters, limiting access to schools or other targeted areas via channelized entry, metal detectors and similar passive measures are the first step. Being able to effectively lock down classrooms and other sub-geographies is also necessary.
Sometimes none of these work, or the area under attack isn't conducive to isolation, and that's where intervention is important. The FBI teaches Run, Hide, Fight when thrust into an active shooter situation, and data shows that the best way to fight is with a firearm. The current strategy of limiting ammunition magazine capacity to force reloads where the shooter can be physically restrained is untenable and hasn't been shown to be effective as an active response with a firearm. It suffers from fatal flaws: that the pool of potential victims includes someone that is brave enough to physically attack the shooter, that the brave person isn't among the first shot, that he or she is lucky enough to be in a close enough position during a reload and that he or she is physically capable of restraining a shooter. The biggest flaw, however, is that this tactic requires at least 10 shots to be fired with up to ten dead victims before there is a chance to stop the shooter. We've seen with both the Uber driver and Philly barbershop that CCW holders are not so restrained and can act quickly and effectively enough to stop a shooter with no innocent lives lost.
