The problem really is that no one is sure if mandating school uniforms makes a quantifiable difference. The current published information on the impact of mandatory school uniforms is largely anecdotal. There are few empirical studies showing that uniforms consistently produce positive changes in student behavior. The most confident statement we can currently make is that the concept of mandating school uniforms to improve behavior is still under scrutiny. There are legal issues.
Every child has the right to a public school education.
This guaranteed right to public education cannot be made conditional upon compliance with a mandatory public school uniform policy. Religious messages may not be singled out for suppression, but rather are subject to the same rules as generally apply to comparable messages. When wearing particular attire, such as yarmulkes and head scarves, during the school day is part of students' religious practice, under the Religious Freedom Restoration Act schools generally may not prohibit the wearing of such items. The attempt to avoid gang presence by restricting the wearing of particular colors or signs is only useful for large, well-established national gangs like the Bloods, Crips, and Latin Kings. Many local gangs are not firmly committed to colors or signs and will simply change as various colors are mandated by the school.