Prep schools aren't the only schools who have uniforms, many public schools are making the switch as well. There's the old arguement that uniforms can stifle a kid's creativity. I never have bought into that idea, because even with the most stringent of uniforms there is some style wiggle room, which I'll show you in a minute.
Before I go on, please make sure to read over and make sure you know your school's dress code. If you're not sure about something, ASK. That way you don't waste money on clothes you can't wear, and you're not stuck in the principal's office trying to give a half-assed arguement over some wording in the student handbook.
Most uniforms that I'm familiar with you have a uniform skirt or pants that you have to pair with a white blouse. If that's the case, here are some ideas for blouses that can give your outfit some punch. I know some of them have no sleeves, but Polyvore doesn't always have exactly what I'm looking for. So save those blouses to wear with cardigan or blazer. These all have collars with no prints or logos (another big no-no). The lace shirt can add texture, the tuxedo shirt can add hint of formalness, and the peplum shirt just because I love it. These can also all tuck in, with the exception of the peplum shirt, so again, make sure that's allowed before buying.
Many schools also have a blazer requirement, or will allow you to wear a sweater in the school colors. I chose navy, since that seems t be the most popular option. You can choose from a varsity-inspired cardigan, to a blazer with draped lapels. The last sweater on the right is a dolman-sleeved sweater from Gap. I think this would look incredible over a long-sleeved shirt with whatever else you have to wear on the bottom. I think this isn't probably a true navy blue, but it might be close enough to pass.
I don't remember the exact rule for shoes at my school, except no open toes/backs and they had to be neutral colored. These shoes all are neutrals, but also have an element of style than just some plain brown loafer.
The real challenge in trying to show style in a uniform is with accessories. If you're allowed to wear backpacks or carry a purse, look for something in a fun color or print. An armful of bangles, a statement necklace, knee socks, there's all sorts of great ways to jazz up your look.
