back in the day, my family's truck had one o' them gun racks, too. We mostly kept an axe handle there but it was not uncommon for it to hold a rifle or shotgun (for them quick weddn's ya know). I don't recall it being against the rule to have it on school property, but again, that was some time ago. Seems we had less troubles back then, even with them dope fiends runnin' 'round. We also had less TV and more activities with real social interaction.
And jobs. And social stigma for 'lifestyle choices' and the like.