I was told by a few people when I was in Ireland that some schools have the kids wear kilts.... I don't know. That is just what I was told and I have a photo in a book (photo book of Ireland) of some school kids in kilts as well. I don't know. Maybe it is a special occassion thing?
Some 'all girl' schools do wear some thing like a kilt as part of their uniform.
Men or boys don't wear kilts unless they are doing Irish dancing or are pretending to be Scottish
P.S. as for the hakama thing, I would say do what ever your Sensei says.