Helps being identified.

This article talks about how helpful wearing uniforms can be to the public and to the school.
"I strongly believe that wearing a school uniform is crucial to the way children behave and also affects them academically. Additionally, being identifiable from a particular school reduces the opportunity for students to skip school or get into trouble on the way to and from school", says Laurelinda. Therefore, wearing uniform identifies which school you are from.

http://ehpsblogs.com/year6/2011/02/26/should-school-uniforms-be-compulsory/