School uniforms promote a more peaceful school environment by removing a potential target for bullying. With everyone in the same uniform, kids can not make fun of each other for having less-fashionable brands or for wearing old clothes. It also removes the opportunity for students to affiliate their clothes with street gangs, and prevents girls from wearing suggestive or inappropriate outfits.
Unfortunately, any differentiation among adolescents and teens creates an opportunity for one group to band together and torment those who don't fit in. Differing clothing tastes, budgets and even the way that current fashions fit particular students offer opportunities for just this sort of ridicule and comparison. Though school uniforms will hardly eliminate the problem, taking fashion and the financial ability to purchase new and high-end clothing will remove one oft-used weapon from the bullies' arsenal.
Underprivileged students are often are the subject of bullying because they can not afford to purchase designer clothing. This creates an unfriendly school environment for everybody. With school uniforms in place the name brands are eliminated along with the bullying, creating a school environment that is much more peaceful for everybody.
School uniforms decrease an individual's creativity by preventing them from expressing themselves at school. Promoting uniformity and decreasing creativity does not lead to a more peaceful school environment, it just leads to forced suppression of individual student feelings while in school. Peace and creativity seem to be mutually exclusive in most instances; they are not related to each other.