Minecraft limited to specific times on the basis that guitar practice and all homework has been completed. Any left over (I forgot! etc) eats Minecraft time rather than shifiting Minecraft time to later.
And it isn't that bitter of a pill becuase he polices my iPad time under much the same conditions. Which he enjoys muchly.
We had same results with dd's blackberry lifeline Her problem wasn't homework etc, it was her general attitude/way she spoke/grumpiness etc. Her blackberry was my saviour! She's had it 15 months now and I've only had to take it off her twice in all that time. She literally changed overnight because I finally found my bargaining tool. She now has grown into a lovely lovely teenager. Not perfect, but then who is. It's great when you find what works for you and your child. Took me 12 years to find it! My other 3 children were clearly not born from the same melting pot as dd