Thinking about late shifts ... I managed the second shift, (some 900 employees) at my companies operation in Virginia for a few years. Not my favorite assignment. When times were booming 2nd shift ran AFTER first shift, so my "day" ran from 3 in the afternoon to 1 or 2 the following morning. (the boss has to arrive early and stay late.) When business fell off the shifts overlapped, so 2nd shift started at 11:00 and ran till 9 or 10 at night.

I felt there was NEVER enough time to sleep.

Put up with that stuff for 3 years ...

Anyway, sleep and the lack thereof as applied to teenagers is discussed in a number of studies online here and there:

http://scienceblogs.com/clock/2006/06/everything_you_always_wanted_t.php

http://scienceblogs.com/clock/2006/09/more_on_sleep_in_adolescents.php

http://circadiana.blogspot.com/2006/04/more-on-sleep-in-adolescents.html

So, I wonder what the school nurses and the TEA medical-type authorities are thinking about the effect of a longer day on the student's sleep cycles.