Hey, I have a 2 year old so I don't have experience with older children, but I do know that even at 8, structure is a huge thing for them, and as parents when we are busy, it's easy to take a schedule and throw it out the window.
I would come up with a structured schedule with structured free-time for him. He may be having a huge problem with time management. Age 8 is usually when the schoolwork starts getting harder, they get more homework, and teachers put more responsibility on them.
Have a system of rewards...for example..."Here is your two-hour block for homework, and when it's completed you get 30 minutes of TV. If you get your work done early and CORRECTLY, I'll make you some popcorn, let you play a video game with your remaining time, etc."
Also, reward him for doing things ON HIS OWN. If he takes a bath, brushes his teeth, and lays out his clothes on his own for 3 days in a row, reward him with a movie on the weekend..after a few days, increase it to 4, and so forth.
I think, that the fine motor skills thing can possibly be with him just being bored, frustrated, and not wanting to do what he needs to do. He obviously needs to be evaluated to be sure.
I could be way off base, but if it was my cihld, this is just some suggestions.
I am also a firm believer in not allowing a child to participate in after-school activities unless their schoolwork is up to standard. School should come first....always.
Oh, and never forget to thank him, thank him, if he is quiet for several hours and allows you to study and how proud you are of him for giving you that time.
I wish you luck!