For those that mention that it sounds strange for carry to be against the law at a school function, off of school property, it is that way in some other states. It would be illegal, for example, to conceal carry a firearm at the San Antonio Zoo while a field trip was being held there.

A person commits an offense if the person intentionally, knowingly, or recklessly
possesses or goes with a firearm . . . on the physical premises of a school or
educational institution, any grounds or building on which an activity sponsored by
a school or educational institution is being conducted, or a passenger
transportation vehicle of a school or educational institution, whether the school
or educational institution is public or private, unless pursuant to written
regulations or written authorization of the institution.
Tex. Penal Code ? 46.03(a)(1).