Welcome to OCDO!
--Make sure you are intimately familiar with firearms laws in your state. Consulting an attorney would be a good thing to do, to make sure there is no backwoods statute or law that can be applied to regardless of your legal right to carry.
--Once the determination has been made that you are completely and wholly legal, carry a high capacity digital audio recorder on you at all times. Ensure that it is on well before you arrive at the school. A secondary one for backup, may be prudent as well. (Ok that's just me, I'm a stickler for redundancy....)
--Bring copies of state laws and regulations for clarification purposes when queried by law enforcement personnel. Sometimes they simply don't know, and you may be opening their eyes to something they didn't even realize existed.
--ALWAYS comply with law enforcement while asserting your rights. Let them know, if or when they detain you, that you do not consent to searches, nor the unlawful detainment.
Others will chime in with great advice I am sure.
Have a good day!