[nkurz]

I'd guess was fairly common in the rural US anywhere that an after-school hunting trip was common. This has probably always been a relatively small but non-zero percentage. I wouldn't be surprised if it still occurs in some communities.

Anecdotally, growing up in Northern Wisconsin in the 1980's, storing guns in lockers would not have acceptable, but this was a non-issue because many students drove themselves to school and would keep their hunting guns in their car rather than bringing them inside. It's possible this it was officially forbidden to have a gun in the car on school property, but in the absence of other circumstances wouldn't have been any cause for concern.