hmm. you can give him the tools. a lot of times, this kind of thing leads to an add or adhd diagnosis...
one thing that i try to remind people these days about this kind of behavior is that schools are getting their hands more and more tied because of the requirements that are more strict (no doubt due to no child left behind) so things like recess, gym class, and other outdoor playtimes or activity times have been cut, thuogh you would know about your school if those things have been cut.
kids who arent able to be active enough during the day, or just throughout their whole lives, they will act sort of off task, or scatterbrained... kids need activity.
so, in my opinion, you have done the right thing by taking away tv and wii privileges, but add to that at least an hour after school outdoor activity. encourage him to run around, chase bugs or whatever you have to do to get him wore out! kids who run outside every day sleep better, get better rest, and function better the next day. it might not be the perfect cure but its an idea.
my little brother who is now 15 had the same problem when he was younger. he wouldnt hand things in even when he did do them, sometimes because he had finished them too late and wouldnt get full credit, and hes still struggling. we arent sure what the issue is, but theres a variety of different struggles kids may have. activity is one of them, another is not being challenged by the work, or being challenged so much that they give up. try to find out what the deal is. see if he is receptive to homework time WITH you or dad. if a kid hasnt been guided about how to do the homework and stay on task, sometimes they cant figure it out on their own. helping him with every problem, making sure hes gotten activity during the day, and give him a great after school snack, like apples and peanut butter, for lots of good energy! more fruits and veggies the better! :D
good luck. ive seen what my mom has to deal with when it comes to this kind of homework issue. for a while in elementary they DID go into his desk every day after school, cleaned it all out, made sure he had all his homework out and all the corrected assignments.
anyway. just dont be too upset at him about it, it might not be something hes doing on purpose. be responsive to him, dont pressure him to talk about it, but do try to stay connected to him in general and let him know that he can always come to you. its hard to get a kid to tell you he did poorly or didnt do homework if he knows hes going to get in big trouble. not to say there shouldnt be repercussions, but they should make sense and not mean you will yell at him.
i dunno.
good luck