Literature and research on sleep is quite confident in speaking about the middle cluster; actually much research into children has that particular skew. We're in the game here with outliers in the first place and research into gifted sleep patterns shows a much flatter distribution of sleep needed. One reference places about 20% of gifted kids needing significantly more sleep and about 20% needing significantly less sleep.
Anecdotally it sounds fine to say that kids keep themselves up by dint of will, but my parents' experience ran counter to that. I was sleeping 5-6 hours a night by age 9. If I went to sleep at 9pm, I was awake at 3 in the morning. I spent a lot of my childhood mornings playing for a couple or more hours while everyone else slept.
