Absence from school was the highest risk factor among the young offenders questioned in a survey by the National Association for the Care and Resettlement of Offenders. These findings, to be published next week, will add weight to the Government's forthcoming policy on social exclusion.
The report, Wasted Lives, estimates that juveniles cost at least #163;75,000 each to keep in prison for a year, and argues that early intervention to support families, raise educational achievements and address truancy and exclusion would be more cost-effective.
The research, conducted with the Prince's Trust and accountants KPMG, tried to identify factors involved in offending and to seek alternatives to custody.
The life histories of 45 inmates from three young-offender institutions showed that having friends involved in crime came second to absenteeism as the main reason for going off the rails. A majority had friends who were regularly in trouble.
Family instability and disruption was another reason, with most having a history of care or social work contact.
Just under half the young people described some level of violence in their family; more than a third said their families were involved in crime; and only four of the sample reported that they were the first in their family to have committed an offence.
Leisure time was equated with nowhere to go and nothing to do - most activities were unaffordable. "For many of our respondents, criminal behaviour and leisure activities were difficult to distinguish and, for the most prolific offenders in our sample, offending was very much a 'lifestyle' matter," the researchers concluded.
The report found levels of drug use were higher than average, but only a minority appeared to have serious addiction problems.
NACRO concluded that Pounds 3,000 per family spent on an intensive support programme to improve family relationships had prevented children at risk being taken into care and becoming delinquent - so saving up to Pounds 62,000 for an offender.
Spending between Pounds 4,500 and Pounds 7,000 a year would reduce school exclusion and help youngsters into work and further education. This could save Pounds 75,000 a year by preventing one youngster from becoming a persistent offender.
Wasted Lives,NACRO, 169 Clapham Road, London SW9 OPU, Pounds 7.50.