Every principal's office should have a instant open (biometric and push button pattern, as well as slower methods) safe with a few easy to use carbines (short rifles) with optical sights.

To take one of many examples, yet another autistic shooter who seems to fit at least some of the patterns in this, the administrators and teachers at Sandy Hook were entirely willing to die to protect their charges (per the official story). Which did neither of those groups any good.

Somehow, though, this sort of thing is "unthinkable". Just as school shootings were unthinkable in my father's days, when in the late '40s/early '50s lots of kids took a gun to school and stored it in their locker, to save an extra trip for before or after school hunting. Only a few years younger than my father Supreme Court Justice Scalia related in the Heller oral arguments that he would carry his .22 target rifle on the NYC subways to and from the range.

Various things have changed since then, and in this area nothing good.