Answer:
For:
Makes the school look smart.
Gets you used to wearing smart clothes because you'll need to wear them when you get a proper job.
It seperates the students from other schools and 6th form students.
It can give you a sense of belonging.
Makes everyone equal, no-one feels jealous as they can't afford designer clothes etc.
Againts:
It can be costly.
Students might not wear it properly.
It's regiment.
It may be uncomfortable.
Some work places don't wear a uniform so people you don't need to get use to uniform.