I didn't wear a uniform, but had a strict dress code (no jeans, no sleeveless, skirts below the knee, no logos, no pictures on clothing, shirts must be tucked in). I didn't like it at the time, but it didn't hurt me any.
As a high school teacher, I am extremely pro uniform. Not just because of the income disparity issue, but because of the gang affiliation problems, and because of the modesty issues.
We have a dress code (much more lax than the one in the private school I went to -- no exposed undergarments, no headwear except for religious or medical reasons, no exposed midriffs). It is truly a DAILY battle (multiple times a day, in fact) to enforce this dress code. We have girls who come to school in shorts with their butt cheeks hanging out and thong straps pulled up above their hip bones while the shorts are low rise. They know that these kinds of things violate the dress code, but because it's dependent on teacher enforcement, they try to get away with what they can. Most of the male teachers don't feel comfortable enforcing the dress code with girls (except, perhaps, for headgear). They feel uncomfortable saying (and perhaps rightly so), "Hey XYZ, your outfit is violating the dress code -- you need to go put a T-shirt or jacket on in the bathroom." The girl would likely become defensive and ask the teacher what was wrong with the outfit. He would then either have to back down or explain that he could see her undergarments, at which point she would probably feel uncomfortable that a male teacher was looking at her undergarments.
Not to mention the problems this kind of dressing creates for extremely hormonal adolescent males. I can imagine it is *quite* hard to concentrate on school work in an environment where there is so much cleavage and provocative clothing.
So, uniforms would not only equalize students, they would create an environment more conducive to learning and wouldn't waste instructional time arguing over things like underwear.