I should clarify that it's not because he doesn't understand. He's VERY smart. He gets it. In fact, he already skipped one grade and his teacher has him doing even more advanced work. He just sits there staring at the paper spacing out or telling me random stories that come to mind. I have to remind him every couple of minutes to continue working. Then he gets frustrated because it takes him so long.
I tried just letting him turn it in unfinished thinking that he'd be so upset about getting a bad grade that he'd never do it again. That didn't work. He knows he can pull the grade up with tests. I tried taking away all privileges until he got it done. That upset him, but he still went slow as molasses. His teacher said he does the same thing in class. She's taken away recess and even isolated him from the rest of the class.
I'm at my wits end!! Why does he do this? What can I do to make him motivated to go faster? All of his smarts are going to get him nowhere in life if this is his work ethic.