Ahhh, I see.
Everyone has posted good ideas here.
I agree with-them.
You have to break the tasks into tiny pieces. My difficult child is the same way. Incl. the rewards.
He just gives up.
It has taken me upteen gazillion yrs to figure this out!
You have to follow him every step of the way, but maybe turn your back and pretend you're reading a magazine or something so he doesn't feel like you're shadowing him. Then you lacadasically say, "Did I hear all those pieces of silverware go into the dishwasher? Just wondering."
I used to say, "Hey! You didn't finish!" and he'd blow up.
(easy child, on the other hand, would say, "Oh," and come back and do it.)
We also have him do homework at school, right after school, with-some of his peers in a classroom. The daycare ladies let the kids play games after they've done homework for about 20 min. (and they eat a snack) That really cuts a huge chunk out of the homework, and difficult child figured out that if he finishes all of it at school, he gets to play immediately when he gets home.
Also, I've learned to cut his homework into chunks when he gets home. (If he still has any.) I used to have him to math, take a break, then English, etc. But now I have him do half his math, then the other half, then half his English, etc. I kept doing smaller chunks, which drove me nuts, because it was an all afternoon/evening thing, but it stopped the meltdowns so that was worth it right there.
Kids like that just don't understand the expediency of doing it all at once and getting it over with. (And maybe they don't have the attention span, either. That begs the developmental testing question.)
You've got to keep giving him the puzzle pieces, and trying new rewards and taking away privileges until you find his triggers. What you're doing now is only partially working because you haven't gotten into his head.
Does that make sense?