Lights out

Pupils who read all night long may be very sleepy in school on the next day.

A useful function for Sugar could be a scheduled "Lights out" time as in a boarding school. The function probably would have to use the school server as a time server.

During the night the laptop could refuse to display anything but a clock.

Exceptions

Pupils could be allowed to use the laptop at night during a limited number of exceptions. Mentors should be able to monitor exceptions in order to be able to discuss potential problems. Night-time use of the laptop can be used as a scarce resource and be used to train responsible use. (A psychological effect of prohibiting night-time use entirely could be to make it artifically interesting instead.)