Maybe this has been said, but I don't think that uniforms in and of themselves will make a huge difference, nor will they immediately.
It has to go with a whole philosophy and be part of a bigger concept. My DD's school had been wearing the uniforms for 100 years and they meant something. Kids were proud of them, whether they wanted to admit it or not, and they had come to stand for a love for their school.
You just don't stick uniforms on a kid and expect things to change overnight. You have to include a new sense of school pride and self worth as students of the school.