Can a school principal pat down student in his office alone?

No, a school principal should not pat down a student in his office alone. This would be a serious violation of the student's Fourth Amendment rights (protection against unreasonable searches and seizures) and could also constitute assault and battery. A pat-down, even if done with good intentions, requires reasonable suspicion of a specific threat and should generally be conducted by a trained official, possibly with a witness present, following established school policies and potentially involving law enforcement. The principal's authority is limited and does not supersede constitutional protections.