Our DS 11, also 6th grade does exactly the same thing. In bed by 9:15, but stays awake about an hour, sometimes more. I've been debating letting him stay up later. I even started reading to them before bed like in the old days to see if that would help soothe him. It doesn't seem to make a difference, but they like it, so for now, we're doing it.
He wakes up at 6:30 for school and proably about 1/2 to one hour later on weekends. He rarely seems tired during the day.
I suspect he's just thinking. I remember doing that as a kid, and as an adult before I had kids and became a person who's exhausted all the time.
Thank you for sharing your story. It makes me feel better about our son. Hopefully my post does the same for you.
