That’s good to hear! When I was in elementary school our parents were asked to buy dictionaries for us kids. We learned how to use a dictionary and I found myself using mine all the time when I read challenging books.

Other things you might consider for your precocious son are puzzle and brain teaser books. I used to love doing challenging puzzles. The books by Martin Gardner can be very mathematically rich. I haven’t read them myself but they were recommended to me by a retired high school math teacher who taught the intro to math education class I took. I plan to eventually acquire a large library of these sorts of materials, once I’ve graduated and have more time, money, and space.