I allow my DS9 to do "math" computer or Plato science or word process (he's currently doing NaNoWriMo. Plato or writing is self limiting. He won't do either of those for too long. He is on timer for most other online education activities. Usually 15-20 minutes per activity, and he doesn't do them every day. He gets 20-30 minutes of recreational Wii or computer time daily. And he rarely if ever watches TV. Maybe an occasional movie on the weekend. He'd rather have time to surf on the internet.
My son's behavior is negatively affected by too much screen time as well, so YMMV! I'd limit any activity that makes him ornery. I want him to have lots of time to interact with people and work on social skills too.
