I don't have any advice, but your DS sounds like mine! They have a few times throughout the day where they are responsible for completing work on their own. He got in trouble for not finishing his "centers" (math & reading), but turns out he was spending too much time on what interested him - the computer! When I talked to him, it was the same reason. Either it was too easy and he was distracted, or he wouldn't start it because in his mind it was too difficult.

You're not alone!!