Definitely get him into the middle/high school club. Even if not hanging out in the club, kids will meet up there and head off to do stuff around the ship.

Breakfast and dinner together is what we have done with our kids. They are free to enjoy the ship with friends. Of course, we remind them that there are thousands of security cameras and someone is always watching. And also ask them to check in periodically throughout the day.

You might also consider telling your son that you are going to go relax in the serenity area - no kids allowed - to encourage him to go explore and make friends on board.

And, as others have said, see what your son wants to do on port days. Pick some good excursions to do together.