I do not have the answer. Every kid is so different.
Wanted to put my two cents about computers/electronics in general. Both of my kids own laptops, so it is very, very easy for them to be online constantly. The rule we have is no laptops in the bedroom Sunday night till Friday afternoon (when done with anything that needs to be done). They are welcome to use them, but is has to be on the main level of the house (they usually leave them either in living or dining room, but the house is very open so you can't really hide on the main level).
It has really done wonders as far as limiting their online time. They are both quite busy with after school things anyway, but the fact that you have to be online while mom is nearby is somehow bugging them.
The same goes for cell phones - they leave them downstairs upon return from school. My daughter used to be on the phone with friends forever, until we decided that while at home she is supposed to use the landline (still have one). The amount of calls has diminished by good 80%.
