Young offenders will be ordered to go to bed early under strict new rules announced by the justice secretary.
Chris Grayling has announced that 15-17 year-olds in English institutions will have to be in their cells with lights out by 10.30pm.
"In some prisons young people are allowed to go to bed when they please. I don't think that is right. Stopping this inconsistency and introducing a strict 'lights out' policy is all part of our approach to addressing youth offending," the justice secretary said.
Teenagers who refuse to obey the new rules will be penalised and lose privileges such as access to a television.
More than 800 under-18s are serving custodial sentences in young offenders institutions.
Mr Grayling said: "It is also crucial that young people, most of whom have had chaotic and troubled lives finally get the discipline so badly needed to help turn their lives around.