Does he like sports? Matt Christopher has a seemingly endless series of books about kids and sports. I have "reluctant readers" and they all enjoyed these books. They would be quick reads for your son but are age-appropriate and there are literally something like 75 books.
How about Judy Blume and more Beverly Clearly? Tales of a Fourth Grade Nothing, Super Fudge, Otherwise Known as Sheila the Great, and the Beverly Cleary "Henry" books are all favorites in my house. I also really enjoyed the Encyclopedia Brown (the kid detective) books when I was around that age.
ETA: our elementary school (K-2) did The Incredible Journey of Edward Tulane as its "one book, one school" selection last year (parents and kids read together). It was a great story but a little heavy and rather sad in parts. If you read it, it might be something to read together. The school is starting The World According to Humphrey tomorrow for this year's one book, one school selection. I don't know anything about it but you might want to look into that too.