One of the main arguments for wearing uniforms it that it reduces bullying since children whose parents can't buy them all the latest fashionable clothes won't be picked on by others. While this is true to some extent, kids can still be picked on for wearing their uniform the 'wrong' way. In some schools it's de rigeur to wear your tie very short, in my school you were laughed at if your skirt was too long (yes, I know how bad that sounds). Kids can be laughed at for having the wrong school shoes or the wrong trainers for PE. The fact is the kids will find just about anything to pick on whether they wear uniform or their own clothes.
A more practical and valid argument about uniforms is the cost involved. Depending on what school you go to, uniforms can vary greatly in price. Some school uniforms are only available for specific suppliers and the rules state that every item of uniform - tie, skirt/trousers, jumper, blazer etc. must be in the school style. This can work out to be incredibly expensive, especially as children tend to grow out of uniforms rapidly. But even if the uniform is a more simple style with regular black trousers and white shirt that can be bought from Asda or Tesco, children are prone to ruining their clothes easily and new uniform expenses mount up. However, the same could be said of their own clothes if they wore them to school.
Uniforms have the added bonuses of making it easy to find children on school trips and also of identification when a child has misbehaved out of school and it seems as though they are going to be around for some years to come.