Whatever your child is doing this summer, encouraging him to write about his life will be good for him. Some kids are natural writers and we as parents want to keep them interested and growing in the skill.
But all kids need to write--a journal can be just the ticket. It doesn't feel like school work. He can draw or cut and paste, write about field trips, vacations, reunions and visits with friends and relatives. He can tell about a fishing trip, a campout, Fourth of July fireworks, whatever he does, or wherever he goes.
A journal is a place where he can record all the fun he has during the summer. It will make a great keepsake and should afford enough practice to keep the child fresh for writing classes in the fall.
Try this article on journal writing to get your child started.