My wife teaches 1st grade and has training in remedial reading. There are number of things that could be causing his problem. Most important is that you take an interest. I hear her talk over and over about parents that refuse to read to their kids and read very little themselves (Kids need to see their parents read). Your school  has a specialist, may be several that work with problems like this. There are state and federal mandates and funding for this. Use the specialists and do what they say and more. Making reading fun is just one part of the puzzle but  Hank the Cow dog was a great series.