I actually like the idea of joining in a musical group like ashley has suggested, if your DS likes music or plays instruments. Also, maybe sign up for camps that involve math or reading or science or any subject that your DS is interested in. There your DS will find kids who share the same interest as he. He will most likely make friends there.
My DS6 is not so good at sports either. He likes b-ball so we signed him up for a b-ball league, for the main purpose of having him learn how to play in a team environment and improve his social skills (he has a hard time making friends with his own age kids). We are starting next week and we'll see how he does. His piano teacher also suggested that he goes to a conservatory prep school on weekends to have master class with kids close to his age and study music together. That would help him with social skills and working with a group too (as ashley's DS has proven true :-))
