It takes a great deal of energy and water to produce clothing. School uniforms represent a significant proportion of your back-to-school spending, so it's well worth buying sensibly or considering some alternatives to buying clothes off the rack.
See if your school has a uniform clothing pool or second-hand shop, or set up a hand-me-down system with other families. You may be able to sell unwanted items through your newspaper or online. If these aren't options, donate unwanted items to a charity instead of throwing them away.
If your school doesn't have a uniform, choose clothes carefully for everyday school wear that will last and that will mix in with existing wardrobe items. There can be great finds in vintage and second-hand clothing stores, and swapping items with friends is another option. Give away clothes that don't fit or aren't being worn anymore.