He has been rewarded for bringing home scores of 85 percent and above, and he receives a consequence for lower scores. He has a daily checklist that includes the activities he needs to complete: homework, practicing his instrument, making his bed, brushing his teeth, and getting his lunch and school clothes ready for the following day. His consequences for not completing the list are no TV, no Nintendo, and no friends. He still doesn't care, and nothing seems to work. Any suggestions?
You may also want to use his sports involvement as a reward to work towards. For example, your son may have no team involvement unless he earns it; he may join a soccer team if he has all A's and B's on his interim report card; and he may go to practice if he has his homework completed in time.
Try changing the routine for studying at home. What would happen if he turned in homework without going back constantly to make corrections? His grade might be lower, but that's a logical consequence of making mistakes. When he has a test scheduled, study with him for 15-20 minutes each night for the week preceding the test instead of him trying to do it all in one or two nights.
Since his inattention and focus problems have been ongoing for a couple of years now, you may want to talk with your pediatrician to find out if your son may be experiencing negative consequences for something over which he has little control.