My nephew's friend wore his kilt to school in Woodbridge, Va. The school told him it was a costume and he had to go home and was forbidden to wear it. That school is just a few miles outside of Washington DC. They have students from all around the world, who wear native clothes, not considered pants.

Bear in mind, I heard this from my brother, who heard this from his son. By the time the information gets to me I can no longer verify the details.