If you want a totally self-driven science thing, have a look at
www.superchargedscience.com. It's a homeschool science curriculum, but its for kids to do on their own. They watch the video, print out their shopping list and then do the experiments on their own. If you sign up for the newsletter you get notified when there are free ones available too. My son loved making the hovercraft and doing other tricks and experiments around air pressure for example. And all without my interference. I love it for that purpose!
If you want task-driven maths that is fun and sets specific goals try
www.dreambox.comFor writing etc practice I'd suggest getting one of any readily available workbooks from 1st grade up for writing, poetry, creative writing - he can do the writing in a fun and engaging way, while still doing his own desired tasks.
