retired as an educator 3.5 yrs ago--no kids are not allowed to have backpacks at desks as it becomes an issue in movement--you are right about the fire hazard--or an active shooter situation (or drills, which most schools have done for years--one of a series of "codes"--fire, tornado, active shooter, chemical spill--boy, the good old nuclear bomb drills of my school days sure seems simple now).
And you are right Prism about not stopping semi-automatic weapons. I read (almost wish I hadn't) an essay written by on of the ER docs in Parkland FL who described the difference between gun wounds from handguns and those from AR-15, etc--said that basically the AR-15 pulverizes the tissues so not a "wound" per se, but just turning the area "hit" into mush and that surviving that kind of wound is a no-go--just made me sick to even think about.