Teenagers natural sleeping cycle is markedly later than any other age bracket. When I was one, I wasn't allowed to play any videogames past 20:30, and I would often spend the evening reading books by a nightlight. Everyday I cycled for almost 2 hours (at ~20-25 kmh), so I got some regular exercise each day too.
Nevertheless, I would still on occasion go to bed at 10:30 (had to get up at 6:30) and lie awake in bed till 01:00-02:00am.
I had friends who went to school in nearby city - meaning they had to wake up 5:45 to catch the bus every day. Their sleeping schedule changed after few weeks - they went to sleep sooner then me every day and it became "new normal" for them.
Likely, if the school and whole world moved every activity an hour up, you would lie awake till 02:00-03:00.
It is same with adults and same with little kids. When you wake them up regularly determines when they will need to sleep.
People with sleep problems have sleep problems no matter flexible schedule or what.
Not the parent, but I grew up in the North of Scotland where it gets dark between 4-5pm for several months of each year, and as a teenager I could never sleep before 1-2am.
I was always forced to get up early, which of course resulted in me being extremely tired during the day, which negatively impacted upon my life (academically, relationships etc).
Nevertheless, I would still on occasion go to bed at 10:30 (had to get up at 6:30) and lie awake in bed till 01:00-02:00am.