My son never sleeps as well as when he is highly active.. Now that for a kid isn't like it is for an adult, I believe that kids needs several hours of physical activity. When my son went to summer school, he signed up for sports and WOW, what a difference... after several hours of playing, at night, he'd sleep like a rock.. Also, I think different foods can affect a person, is he getting too much sugar and not just sugar, but other foods can make a person jittery (esp if they are showing signs of allergies) sometimes when younger, blatant signs of an allergy haven't developed just yet like a rash or sneezing.. sometimes, the signs of allergies are more subtle as in the case of someone now being able to sleep well ..
so that is worth considering. also, hormone fluctuation... when my son is going through a growth spurt, he can't sleep as well..
therefore, the next time your son has a physical, perhaps you can have them do a hormone blood test, just to see how your son is doing..
lastly, about an hour before bed, if not sooner, begin to dim the lights around the house, does he like to read? tv can be over-stimulating, but reading can sometimes help lull a person to sleep, see if he is willing to read.. going straight to bed (unless dead tired) after watching tv for a period of time is hard to come down from... but if you make the house quiet and calm before bed, I think this can definitely help... even a warm shower may him relax more..
good luck