IMO the trick isn't to stop kids from playing games, but to gamify education. In fact, formal education is already gamified, and has long been so ... but just really badly. You do certain stuff, try to learn certain skills and knowledge, then those skills and knowledge are tested, you get a score, and if it's high enough you get to move to the next stage - but the reward system in traditional formal education absolutely sucks.
Whereas in well-designed games such as high-skill first-person-shooters and the highly-addictive World of Warcraft, you're constantly getting feedback on your progress, and you can really feel yourself advancing, even if it's only in tiny increments.
If similar feedback and reward systems could be integrated into the schooling of children, and indeed into the education and training of adults in any number of fields, I believe the benefits could be staggering. Homework could be something that kids want to do.