Inky, they have levels of television turn-off. Gold level has no screentime during the week. They can have as much as they want (or parents' decree) from Friday afternoon until Sunday afternoon. Silver (what we do) is only a half-hour and bronze is one hour. The kids sign a pledge and then the parents confirm at the end of the year that the kids followed the level they agreed upon.
I like it because it supports what we already did in our house. We know some people where it didn't work (they did Gold level but the kid wanted to spend the entire weekend playing computer games).
They get a little trophy and a certificate at the end of the year.
