I wore a uniform to Catholic School. That was more years ago than I care to admit. Some Catholic schools still require them, and there are some public and charter schools that have adopted them. But, for the most part, American students can wear whatever they want to school.
That is, as long as what they're wearing conforms to the accepted gender norms of their community. Speaking of which: While some parents say that uniforms are a "leveler" (If all kids are wearing the same outfit, none is "cooler" than the others), they also are a way of enforcing accepted gender norms. Typically, males wear black (or other dark-colored) trousers and a white shirt with a plaid tie in the school's colors, while females wear a skirt in that plaid with a white blouse.
In very few countries are transgenders more visible than they are in Thailand. But even in the country that does more sex-reassignment surgeries than any other and whose Miss Tiffany transgender beauty contest is a national event, students are expected to wear the uniform that conforms to the gender on their national ID cards, which is all but impossible to change, even after transition and surgery.
Also, trans females are still referred to as "ladyboys" and trans males as "tomboys", which represents a different view from those in the West regarding transgenderism, not to mention an underlying male bias.
So it is significant that Bangkok university has changed its uniform policy to accommodate trans students.
A "ladyboy" can wear either of the uniforms shown above. On the left is the female uniform; on the right is a modified male uniform with the trousers cut tighter than the ones males wear.
A "tomboy" can wear the modified female uniform shown on the right or a male uniform with the trousers cut a little looser than the ones biological males wear.
Hmm...Do you think Catholic schools will follow suit (pun intended)? Prep schools?