We are in the midst of this, too, and I've been handling it the same way as mnmom and BWBShari - make him do it over and explain the rationale behind doing it well the first time.
The only thing I would add is to have your son take the first crack at deciding what is not up to snuff. My DS has always been surprisingly good at judging the quality of his own work, especially given that he seems to have no clue when he's actually in the process of doing it. So I try to tell him, with every sheet, to check it over for neatness, completeness and accuracy (funny that we use almost the exact same wording, Mama22Gs!).
He catches quite a bit, but sometimes it takes 2 or 3 tries before he catches everything I catch. I have stopped telling him how many errors I see, because then he isn't really examining everything and thinking for himself, so now I just tell him there are errors - and sometimes I don't even tell him that much. I am hoping to help him develop "an editor's eye" toward his own work, but it's a slow process.
