Michelle,
That kind of problems are not uncommon. I would not worry and stress too much about the grades. It matters when he gets into middle school.
I am sure your DS enjoys doing advance levle Math and loathes doing regular boring Math. They tend to be careless with the easy questions or doiing it on purpose. You may need to bluff and say like (he would disqualify the advance class if his grade in regular class does not improve soon, etc...).
You may talk to the school counselor or admninistrator and see if your DS's advance level homework can be counted for the grades. First, you probably need to talk to his teacher. If the teacher goes along with it, it will probably be easier to talk to the administrators.
