This is a major issue for me as I am a reenactor and used to speak in schools carrying a Rev. period flintlock rifle. That is now illegal and I cannot do it anymore.
18 U.S.C. 922(q)(B) says the unlawful possession provision does not apply to possession "(iv) by an individual for use in a program approved by a school in the school zone ... ."
This would appear to cover the reenactment scenario if approved by the school.