What can schools do to the transgendered students about their uniforms?

I will write this from my on experience. A friend of mine went to middle school in Japan. That school also had a uniform to wear. However, she did not like wearing skirts, so she told the teacher that she did not want to wear the skirt. The school allowed her to wear pants on top of sailor shirt, which many Japanese school girls wear to school.
Moreover, when I went to study abroad in Adelaide, Australia, I could choose either to wear pants or skirt. Although it was a girls' school, students who are uncomfortable of wearing skirts were allowed to wear pants all the time. Some students wore both.