Oooh, oooh, oooh! Here is a real school bag, unusual for America, and extremely cool and classy.
Japanese school bag, closed
Japanese school bag, opened
Scroll to the bottom of the page for the description.
For $150, you can hardly go wrong. This looks like a good quality piece that would last your for ages and ages, and I imagine you would be the only girl with one like it at your school. I'd consider replacing my briefcase with one of these, since it can be worn over both shoulders like a backpack. Would be more convenient come bicycling season.