This was a huge problem last year for my GS who was 12. He's now 13, and is sleeping better. He even brought it up at school during his advisory period last fall and the other kids suggested all kinds of things, including Melatonin.
We made sure he got enough exercise and also tried to keep his bedtime consistent, even on weekends. We also let him read in bed. Boring books, as Isabel said above, are the best kind.
It has improved greatly since last year at this time.
For our DS, I think it might have been partly hormonal. He's on the early side for puberty.
He was never a great sleeper, even as a baby. Some people just don't need as much sleep. Is your DS struggling during the day? If not, it may not be a problem for him, other than the tediousness, tediosity (?) of being in bed but not able to sleep.
