The school where I went was pretty strict regarding religion ... this created a sense of discipline however. Similarly to you mephisto, it worked until I left school or should I say it worked after I finished school?
We didn't have any costume, we could dress up the way we wish but respecting what the profs deemed suitable. Once, I wore a Harley-Davidson t-shirt, with one of those bad boys with long hair on a bike, I had to wear it the other way around for the whole day because "those are dirty people with stinking hair" according to my math teacher.
Cheers,