I decided on 'No'.
Uniforms will not be comfortable on everyone. Uniforms have a uniform cut, and not every body is uniform (I remember some of our workers complaining about their uniforms being very uncomfortable in the crotch, for instance). So some will feel physically uncomfortable, while others may feel mentally uncomfortable (a modest girl may not like a short uniform skirt, for instance). If a kid is physically or mentally uncomfortable, he/she may have as much trouble focusing on their work as the kid distracted by the girl with the big boobies two rows over in the fuzzy pink midriff and thigh-high boots. Both extremes can lead to problems.
Instead, I think the middle ground of a dress code is best. It allows a kid to wear clothes they are comfortable in, without going to the extremes, or identifying with a gang or sub-culture.