[AnthonyMouse]

> I thought it was total sleep duration.

They're related. If you go to sleep at the same time (relative to actual-midnight) and get up an hour before school, you get more sleep when school starts later.

Or else what difference would any of it make? If all you did was start school at 9:30 instead of 7:30 and then kids used that to go to bed two hours later, nothing has changed. But when people go to sleep (and are inclined to wake up) has a lot to do with daylight.

[kd0amg]

If you go to sleep at the same time (relative to actual-midnight) and get up an hour before school, you get more sleep when school starts later.

That still doesn't seem all that helpful. If my high school had started at 10 instead of 8, I'd be out of class at 5:30 instead of 3:30, done with fencing practice at 8 instead of 6, etc. I'd finish the night's homework two hours later, and finishing that was already well past sundown even on the original schedule. A later start time wouldn't have been an opportunity to stay up later -- it would have been an obligation to stay up later.

[AnthonyMouse]

The only way you'll be getting more sleep is by doing less non-sleep. You can't add hours to the day. What you can do is to arrange the sleeping hours so that they're the ones that come more naturally to more of the people in that age group.

The total lack of unscheduled time is an independent problem.