My 16 y/o son takes forever to get his homework done, due to his distractibility. Saturday on "Teen Kids News" they shared a suggestion that I think is going to work for him. He should keep a pad of paper next to him when he's doing homework. When a distracting thought enters his head, he jots it down on the pad of paper.
With school about over, he doesn't have any more homework (other than studying for state exams). But we tried the technique yesterday when I gave him a list of chores to do. His dad & I were very impressed with all that he was able to accomplish in a very short time. He even seemed pleased with himself.