Dolsak, that will depend on your state (some states have outright bans on firearms on school property; some allow permit holders to carry; some allow firearms for school functions (rifle team, etc) with permission of the principal).
You can look some of it up on http://handgunlaw.us
You can also try the findlaw website.
What I'd recommend is using either or both websites to determine what agency in your state handles weapons permits, and calling them to ask about the legality of a firearm in your scenario. And, of course, if it's legal, then get your principal's ok.
Edit: Again, I do recommend you also verify what the Master Chief told you with the regional JAG office.
You can look some of it up on http://handgunlaw.us
You can also try the findlaw website.
What I'd recommend is using either or both websites to determine what agency in your state handles weapons permits, and calling them to ask about the legality of a firearm in your scenario. And, of course, if it's legal, then get your principal's ok.
Edit: Again, I do recommend you also verify what the Master Chief told you with the regional JAG office.