Agree with TPM. Creatine is widely used and researched, but understand what it does and whether that fits into your nutrition plan. Creatine is on a very, very short list of supplements that are actually beneficial.
CAVEAT - Get your nutrition in order before trying some "magic" supplement. There aren't any magic (legal) supplements that will overcome a crappy diet. You're wasting your money taking supplements on top of a standard high school kid's diet, so fix that first.