Granted, this was quite some time ago, but I used to go shoot clays with my school principal back in high school over lunch hours, and it was VERY common that guys would come straight to class from hunting in the mornings, or go hunting directly after school, so it was very common that guys would come to school with a gun in their truck...
The police and the school agreed on the policy that students with firearms in their vehicles were required to park in the lot across the street from the school, because it was actually CITY property, even though it was used for school parking. That was the rule according to the "letter of the law". To my knowledge, that's still the policy at the school, although I'd assume that kids are encouraged to be much less vocal about having a firearm in their car than we use to be.