A couple more things:
  Like Artana, we do museums, zoos, & other things on weekends.  Those things will influence the choice of books to read.  I pick some of his books to guide him.  
  GS10 is in the 5th grade and rarely has homework to bring home.  I guess he does it while he's waiting on other kids to finish class work.  I think it's great that he is motivated to do that, but he's not getting a habit of studying outside the classroom.  He's also not self-motivated to dig deeper in maths & science, which I'd like him to do.