TexasCHLforum.com

State law says that you're not allowed to carry "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;" but then adds: "'Premises' has the meaning assigned by Section 46.035," which itself says "'Premises' means a building or a portion of a building. The term does not include any public or private driveway, street, sidewalk or walkway, parking lot, parking garage, or other parking area."

Basically the difference should a school decide to "allow" carrying outside of buildings is that a) you could be able to carry at school events that are held outdoors (as long as you have written permission), and b) if you're found to be carrying, you're not likely to get in trouble with the school and put your education at risk.

Of course, I'm no lawyer, so take this with a grain of salt.