Use the rest of this summer to help your son make some friends. Swimming lessons, activity day camps, and Boy Scout or YMCA activities are good places to make friends without the added pressure of school. Perhaps there are some children in your neighborhood you could ask over to your house to play to help your son make friends. Continue to look for groups in which your son could find friends after school starts this fall.
Talk with the school counselor. She may be able to give your son some individual time this fall or include him in a small group on making and keeping friends. Meet soon after school starts with your son's new teachers and ask for their assistance in helping him with friendship and social skills issues.