Our entire fourth grade does a checkbook system. St. start out with a "bonus" of $50 each six weeks. St. earn or lose money, and keep record of it in their checkbook (I also have a clipboard to record "losses" of money and why/date it was lost). Things they can earn money for are good citizenship, compliments from other teachers or staff, turning in homework on time, etc. Can lose money for talking, not turning in homework, repetitive misbehaviors, etc. At the end of the six weeks, if st. have at least $200 in their account, they get to participate in a celebration activity (varies each six weeks-movie, game day, ice-cream sundaes, etc.). Those who don't have enough are in study hall, usually doing work they didn't finish. They start fresh each six weeks (with another $50). I have everything typed up(how to earn/lose money and the reward/consequence at end of six weeks), and have them sign the "contract", along with their parents Kids love this system, and it teaches them how to keep a checkbook as well.
My local bank donates the registers, by the way.