My 10 year old son loved all the DK Encyclopedia type books too. He has always loved science and technology and this is one of the reasons he sometimes sounded like a little professor when he was younger, before he learned that it wasn't socially acceptable in our sports obsessed culture to talk about the things he was interested in. He used a science encyclopedia for reading practice instead of a reading curriculum at age 5 and 6 because this was what he wanted to read and he was much more willing to read for me if he was interested in the material. But I had people telling me that he needed to read more fiction and I used to let it bother me because I didn't have much confidence in my ability to homeschool my son. His friends tried to talk him into reading the books they were reading, but he refused. He wouldn't even read Harry Potter. He read three or four pages of his friend's Harry Potter book when he was about seven, but he just didn't want to read any more of it, although he did watch the movies. He thought the book he was reading at the time, Johnny Tremaine, was better and he has just never found the time for books he wasn't interested in. He did like historical fiction, especially if it included plenty of historical facts, and a few years later he told me he really liked books like Animal Farm and books that make him think. I am very happy that my son loves science and technology and prefers reading about that instead of some of the books I see his friends reading. His favorite magazine now is Popular Science and he talked me into ordering Wired.
My state does not require testing for homeschoolers and I am curious about what grade level he is at for science and history and even general knowledge. My special ed teacher friend keeps telling me I should enroll him in school just long enough to have them test him but I promised him that I would not make him go back to that school, even for just a few days.
My son uses Google to find online science trivia games and science quizzes on his own and I think some of these have recommended grade levels. If he doesn't get the correct answer on anything he looks up the info, so I think he is filling in some holes that way.
