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What do you think is a reasonable bedtime for 11, almost twelve year olds? DS goes to bed at 9, but some nights it's 9:30.

Depends what time he has to get up, but 10 hours is recommended for this age. Before puberty, most kids tend naturally towards an earlier bedtime and wake-up...before 10 for sure. At puberty, the sleep schedule shifts, which is why we have so many problems with teens wanting to stay up late and being so tired. HS needs to start later than elementary school.

http://www.sleepfoundation.org/article/how-sleep-works/how-much-sleep-do-we-really-need