This does not work with teenagers, in whom bedtimes are practically unenforceable, but whose need to get to school in a timely fashion does a reasonable job of imposing a getting-up time. They are chronically sleep deprived. Smaller children, I imagine, have even less of a chance of managing the feat.
...Woah. Thanks to your comment, I just remembered vividly how much my school years sucked.
Full essay: http://www.gwern.net/Melatonin