The scientific evidence for keeping young people out of prison was clear 20 years ago, but not enough has been done.
Justice sector science advisor Dr Ian Lambie's just released report recommends the adoption of what's called "development crime prevention" to reduce rates of youth crime by focusing on children from an early age and previous generations.
The report said New Zealand had a record high overall prison population, but the number of children and young people under 24 in the criminal justice system had fallen.
For decades, New Zealand research has shown how childhood factors can influence young offending and imprisonment as an adult.
Dr Lambie said the prevention message, arguing for earlier intervention in schools and in homes, was clear 20 years ago.
But since then a new generation of young offenders had grown up. He said recent evidence showed early intervention was more effective and programmes such as cognitive behavioural therapy for pre-schoolers and parenting courses were the most effective.
Early intervention could stop cycles of trauma, offending and imprisonment.
"Research since that time has shown that the most effective - and cost-effective - way to reduce prison costs is to prevent kids getting into crime at the earliest opportunity."
Despite a reduction in the number of young offenders overall, people aged 17 to 24 offend more than all other age groups, the report said, and before young people likely to offend actually start committing crime, they had often already experienced abuse, violence and neglect.
Dr Lambie said there were no quick fix solutions for the criminal justice system but more could be done to work with those aged up to 25.
Strong and courageous leadership required
He said the country needed to think about what sort of New Zealand it wanted to create for future generations.
"Is it one with a rising prison population, at ever higher costs, without corresponding community or offender benefits? Is it one with chronic Māori over-representation in the criminal-justice system? Is it one where children are increasingly both victims and offenders?
"The evidence says it does not have to be so, and it will require strong and courageous leadership to commit to and implement a change programme that produces sustained positive change across the justice system."
The report, which discusses the evidence for reducing youth crime in recent decades, said the science was clear and it was more effective to focus on improving social and family environments.
"Don't believe that they are at the bottom of the cliff at 18 years old - we just need to get better at understanding youth, seeing the opportunity and working more effectively with this age group - we need to understand and appreciate the unique needs of this population.
"The effects of abuse, neglect and maltreatment on children's development and behaviour can be successfully addressed at an earlier stage in the home, at school, in the community and in targeted mental health and other services, for a fraction of the cost of later imprisonment.
"A developmental crime prevention approach can partner effectively with successful cultural approaches addressing the fact that, for instance, young Māori are significantly and persistently over-represented in the criminal justice system, both as victims and offenders and that rates of violent offending by Pacific young people are also disproportionately high.
"Crucially, evidence shows that the younger the child is at intervention, the better the outcome is likely to be," the report said.
Young offenders in prison were more likely to re-offend and be imprisoned again than the general, adult population, the report said.
Dr Lambie's report also said so-called boot camps did not work and, in some cases, military-style schools had been shown to increase crime.