You know the school I'm in now has a mandatory study hour system, that is, everybody is assigned a number of hours that they have to spend after school in study hall, and that number is based on your grades. They're called "Tack Hours," and that's because of how they're read. For example, if you were assigned 15-2 as your study hours, you would be on "Fifteen Tack Twos," meaning you have to do 15 hours a week total, and 2 hours every day preceding a school day. Your total number of assigned hours is based on your GPA:
4.0 to 3.6: 0-0, "Zero Tack Zeroes" or "Vols"
3.59 to 3.3: 10-0, "Ten Tack Zeroes"
3.29 to 3.0: 15-2, "Fifteen Tack Twos"
2.75 to 2.99: 20-3, "Twenty Tack Threes"
>2.75 or after failing a test: 25-4, "Twenty Five Tack Threes"
To be honest I think it's a really solid system. Your motivation for doing really well is more free time to forget around and do whatever, so the more time you spend paying attention and participating in class, the less time you have to be in the school building. If public school did something like this then I'm p sure most peoples' grades would improve just so they wouldn't be stuck at school longer than they had to.