Help your son get involved in some activity at school next year in which he'll have the chance to talk with others who share his interest. If he enjoys a special sport or is musically inclined, have him take lessons this summer so he will feel confident of his ability to handle the activity. If tryouts are necessary, he needs to take the responsibility of finding out when they will be held. You don't want to get in the habit of talking for your son and letting him avoid conversations.
Find out if your school corporation is offering any enrichment programs this summer in which your son could participate. You should also check with the parks department and the local library to find out about their programs. Also talk with parents who have children your son's age to find out what their children are doing this summer. Do help him choose activities that he will enjoy so that he'll want to talk to the other participants.
Before school gets out, make sure your son has the phone numbers or email addresses of some of his school friends so he can do things with them this summer. Make it easy for him to socialize by offering to drive everyone to the swimming pool, park, camp, or movies.
Above all else, help your child learn how to be a social being. He needs to know how to make friends. Show him how to ask open-ended questions that can't be answered "yes" or "no." Teach him to look at people when he is talking to them and to be a good listener. Encourage him to tell jokes and laugh as other people enjoy this. Help him learn how to compliment people. Model these behaviors so he can learn them, and he will feel more confident in dealing with his peers.