"The brain science is sending us some pretty clear messages. We are out of step with the rest of the world by not including 17-year-olds in our youth justice system - the brain science would have something to say about that."
The Youth Court dealt only with offenders aged 14 to 16 until the current National Government gave it authority over 12- and 13-year-olds for very serious offences in 2010.
The previous Labour Government had planned to extend its authority upwards to cover 17-year-olds but National cancelled that change.
Its 2010 law also doubled the maximum term in a youth residence from three months to six months and introduced "military-style activity camps" to be run outside the residences by the army.
Professor Richie Poulton, director of a 40-year study which has followed 1000 people born in Dunedin in 1972-73, told the seminar that the study had found two separate groups of antisocial adolescents: an "early-onset" group whose bad behaviour began before age 5 and continued throughout their lives; and an "adolescent-onset" group who were led into bad behaviour by their peers but grew out of it.
"With the adolescent-onset group, do not do group interventions, because they are peer-driven. The last thing you should do is put them with other young people," he said.
"So boot camps are wrong, prisons are wrong, for that group, and any other form of hanging out together, because essentially what you learn is a lot of new tricks."
Judge Becroft said he was reassured by Professor Poulton's talk because New Zealand's youth justice system tried to keep young offenders out of the justice system where they would meet other offenders.
"Eighty per cent of the young offenders in New Zealand are not charged, they are dealt with by police diversion in the community. They do not come to court, which is the worst place for them," he said.
"There is no country in the world that matches that rate, and it works best. It's just good, firm, community-based creative intervention led by police and the community.
"We do not have boot camps in New Zealand, so I was reassured," he said. "I think we have a system that stacks up internationally."
He said the great majority of offenders whose crimes were so serious that they did get to the Youth Court were "severely disadvantaged".
"Their biggest characteristic is that they are boys, and their next biggest characteristic is that they are not at school," he said.
"Their next biggest characteristic is that their families have some form of involvement with Child, Youth and Family - 79 per cent of them."
The judge said he now saw "pockets of a third-generation permanent underclass throughout New Zealand".
"That's not to say that everyone who is poor or disadvantaged offends, but it's a hugely high risk factor. That's one of the reasons why 79 per cent have a care and protection history. That really worries me."
He referred to the recently published book The Spirit Level which showed that countries with the highest inequality, including New Zealand, also had the lowest levels of child wellbeing and other measures of social cohesion.
