Some 51 per cent of teenage criminals currently in custody said they had not done anything inside that would make them less likely to reoffend on release, the report for the prisons watchdog and Youth Justice Board (YJB) found.
The findings will fuel the debate over the effectiveness of custody after Kenneth Clarke, the Justice Secretary, said he wanted to send fewer criminals to prison.
He has claimed it is “virtually impossible” to rehabilitate someone during a jail term of less than 12 months.
The joint study also found almost half of young girls and three in ten boys who are in detention had no visits in the last month or at all.
It was carried out by the HM Inspectorate of Prisons and the JYB, which oversees youth offender management.
The number of 15 to 18 year-olds in detention fell from 2,126 to 1,724 during 2009/10 and is down 30 per cent in the last two years.
Nick Hardwick, Chief Inspector of Prisons, said: “Prisons can offer a short window of opportunity for the majority of young people who end up in custody.
“This report indicates that there is a foundation to build on in young people’s own realisation of the challenges they face and commitment, at least while they are in custody, to change. That is an opportunity that must not be wasted.”
Frances Done, Chair of the YJB, said: “Custody has increasingly become focused on the most troubled and difficult to manage children and young people in our society.
“The YJB commissioned this report to identify progress made and to identify the areas which need further development.
“We will take the views of young people on board and work with all establishments to provide the best chances and the best opportunities to help young people stop offending.”