My kid got a big boost out of summer programs that challenged her and allowed her to meet other gifted teens. Don't know if he is still in the age group (but I think he is), has the stats, or the interest, but attending Davidson's THINK summer program was huge for my kid both in terms of motivation and making friends. She is a freshman in college, and still talks via phone with one of her THINK friends every couple of weeks, and is linked up with others online.
Or he might want to try to do something over the summer that he is interested in finding out more about (maybe asking local professors if they need research volunteers over the summer, or attending a summer program in something he is interested in like engineering).
The school club thing is a good idea. We asked our kids to participate in some kind of support and expected some kind of club participation as well -- just what we expected, and they did it. D2 did club fencing outside of school as her sport and met kids like herself. She also was in Quiz Bowl, another good activity for a gifted kid. And he school started a FIRST robotics team her junior year, which she also ended up enjoying after a couple of male friends talked her into joining.
