School sponsored activity, carry is a no-no.
An equivalent situation would be going on a field trip to the zoo with a bunch of students in your private car, to meet other groups of adults and kids for the same event who arrived by school bus. You can carry in your car on the way there, but the other adults on the bus cannot carry. But even if the facility were not posted 30.06, you would not be allowed to carry once you went into the zoo as part of the school activity—whereas, I and my family who were not part of that activity could
carry into the zoo at the same time......if it weren't posted.
All of this said, I might be full of wind and wrong as heck; but that is my understanding of the law.