"Logan police arrested Marcum at the school last Thursday after he refused a teacher's order to remove the shirt. White says prosecutors are reviewing the case to determine whether to file charges.
Marcum has said that he was arrested on charges of disrupting an educational process and obstructing an officer, though White said Monday that the Logan County prosecutor's office is reviewing the case to decide whether to proceed."
http://www.oregonherald.com/bnews/story.htm?id=580
So there you go folks. He was not arrested for wearing an NRA t-shirt.
I can't believe they are being obtuse about this.