Schoolgirl uniforms are the central part of many of fetish fantasies. In the western world, these fantasies revolve usually around the structure and punishment known from strict English schools in the 18th century. In Japan, where kids to this date are required to wear uniforms in most schools, school girl fantasies are even more common than in the western world, usually revolving about (slightly modified versions of) the standard uniforms.
One common misconception of schoolgirl play is that it borders on paedophilia. This is very rarely the case - most people in the BDSM community derive pleasure from the rules and punishments for misbehavior instead. In many cases, men are forced by their femdom into these uniforms as part of feminization play.