Keeping young criminals on the straight and narrow is being made harder by councils' failure to provide a full-time education to those excluded from school.
Most local education authorities in Wales are still failing in their legal duty to provide excluded children - including young offenders - with 25 hours of education a week, according to a new report from inspection agency Estyn.
It came to a similar conclusion in another report on youth offenders published last year.
Chief inspector Susan Lewis said: "Many young people under the supervision of youth offending teams (YOTs) are permanently excluded from schools. Too many of them do not receive the recommended 25 hours a week in their alternative placements.
"This has a negative impact on their life chances and hampers the efforts of the youth justice system to reduce crime."
Estyn found that last September there were 1,747 youth offenders being supervised in the community by 13 of Wales's 18 YOTs.
Around a quarter of offenders of statutory school age were receiving less than the required 25 hours' education a week.
Nearly a third of all young offenders aged 10-19 were not receiving any education or training at all - rising to nearly half of all 16 to 19-year-olds.
The report found that most young offenders have poor basic skills and behavioural, emotional and social difficulties.
Half had been in council care at some point while almost a third have mental health problems. A third of the girls and a quarter of the boys had also suffered violence at home.
Estyn criticised government bodies for not collecting data on the educational achievements of young offenders, and noted that occasionally schools are reluctant to pass on assessments and other information to YOTs - and even to transfer the funding for an excluded pupil moving to alternative provision.
Inspectors found that young offenders need a great deal of targeted support if they are to achieve the educational levels of non-offenders.
But when they do gain recognised qualifications or improve their behaviour, confidence and self esteem, they are more likely to reduce their offending and get and keep a job.
The report also highlights the need to give better support to girls. Many have been sexually abused and have low esteem leading to self-harm, making placement more difficult.
But the report highlights projects aimed at tackling the problems, and praises a greater willingness "to work in partnership to the benefit of the young people in the youth justice system".
The Assembly government has funded a one-year pilot project in Bridgend and Denbighshire to provide support to young offenders when they are in custody and after they are discharged.
Both areas have appointed full-time youth officers, who work one-to-one with young offenders to assess their needs and try to engage them in education and training.
Mal Gay, manager of Bridgend YOT, said: "We hope that the funding will continue after the pilot ends. Otherwise these young people will be dropped back into a black hole."
Stephen Wood, of Conwy and Denbighshire YOT, said the project had long been needed.
"It will be collating valuable data about the scale of the problem. But the scheme needs to be rolled out to every YOT area in Wales," he said.
The quality of education and training provision for young people in the youth justice system, www.estyn.gov.uk