When you sit down with him to help him do his homework - what is it like? Does he have trouble staying on task? Can he do several problems in a row without losing his concentration. Does he have a clue how to do his homework? When he was doing his homework, did it take him a lot longer than the other kids in his class?
If a child is doing poorly in school - ie. everytime they are called on, they have the wrong answer. Every test or quiz they take, they fail it. It doesn't take too long to start hating school and want to stay home. Frankly, if you don't know how to do your homework or if it takes you forever to do - then you learn, "why bother"!
Finally, what is his teacher saying? Is it the same thing his teacher said last year? have his teachers remarked that they give him directions and he can't follow them. Does he finish his tests on time, take forever, or just give up? Does he have trouble on the playgrounds. What do his teachers say? If he is fine at school, then the problem lies at home. If he is having problems in both areas, then you may well need professional help for him.
Talk first with his teacher, and then with the school psychologist. You also might want to check out the ADHD site on this forum and particularly this link which explains ADHD.
If you have any other questions please post here or on the ADHD forum. Good Luck