Hire an honorably discharged/retired vet with some arms experience - 2 or 3 at every school on patrol. I wouldn’t trust teachers - mainly because they are at work in a classroom and not on patrol.
Here’s Real, they need one entrance in the morning with 2 metal detectors and 2 police K9 units standing by while facility monitors the metal detectors. Criminals fear dogs. Any student walking by them each morning would think about that.
And so many of them are progressive weenies, too.