To increase your son's motivation to read, try setting a time aside when everybody reads in the house. You can read the newspaper or a book of your own while he tackles his own material. Have a look at guysread.com. It gives many ideas to motivate boys to read and includes recommendations of books that boys have liked. Be careful that the reading level is a comfortable "fit" for him. What is your son interested in? Would he read comic books? Sports Illustrated for Kids? Have you tried listening along with him when he has books on tape?
Have you tried a reward system? Track the number of times your son reads for 15 or 20 minutes on his own or with the book on tape. For every time he does this, give him a check on a chart. When he has collected a designated number of checks (e.g., 5 or 10 checks), he can trade them in for a reward of something he would enjoy doing. Part of the fun of this is finding what would motivate him to do this work. For some kids it's a trip to McDonald's. For others, it's time on an outing alone with Mom or Dad.
There's another important issue you've brought up: helping your son to understand his learning disability. Try these suggestions:
1. There's a wonderful book written for kids your son's age called Keeping Ahead in School by Dr. Mel Levine. There's also an accompanying tape with Dr. Levine reading the text. The book is divided into chapters that discuss different kinds of learning disabilities and how they can apply to different kids.
2. Try talking to your son's teacher and/or guidance counselor and see if there is any kind of organized program to teach kids in your son's school about their learning difficulties and, even more important, teaching them to advocate for themselves so that they get what they need in school -- and in life.
3. If there is a branch of one of the many advocacy groups for children and adults with learning disabilities in your community, one of them might hold meetings for teenagers. Try contacting the Learning Disabilities Association of America at 1-888-300-6710 or the International Dyslexia Association at 1-800-ABCD123.
4. Finally, if your son knows how to use the computer and access the Web, there is a wonderful website for teens where your son can ask questions in private and get answers from professionals and from other teens with similar problems.