The traditional "boot camp" for young offenders was "arguably the least successful sentence in the Western world", the principal Youth Court judge says.
"It made them healthier, fitter, faster, but they were still burglars, just harder to catch, " Judge Andrew Becroft said.
He said physical programmes backed up by mentoring and family support could work, but New Zealand's corrective training camps, which ran up till 2002, found 92 per cent of young attendees reoffended within a year.
"It was a spectacular, tragic, flawed, failure," he said.
The Government's proposed military-style activity camps, introduced this month as part of its 100-day urgency plan, has worried some justice and youth experts, who say overseas and local experience show military-style boot camps do not work.
Judge Becroft made it clear he was not commenting on government policy, but said any debate on the merits of a so-called "boot camp" must be clear on what was being discussed.
An outdoor, physically challenging programme run by quality instructors, combined with intense family therapy, drug and alcohol counselling, education and other support could be beneficial.
Kim Workman, of Reducing Crime and Punishment, said American experience showed that when the military-style "short, sharp, shock" approach was combined with mentoring and after-care, it still made no difference at all.
A physical programme based on a therapeutic model could be beneficial, he said, and there were already a handful of outdoor-based programmes in the country that were working well.
Social Development Minister Paula Bennett agreed the old boot camps lacked the necessary follow-up support to work.
But the Government's proposed military-style activity camps would be followed by six to nine months of intensive mentoring, she said.
"At no point are we going to throw them in there, get them fit, beat them around a little bit and send them back on the street, that's just not it at all."
Ms Bennett has said the three-month camps for the country's 40 most dangerous young offenders would use army-type facilities and training methods to teach self-discipline, personal responsibility and community values as well as literacy, numeracy and drug and alcohol support.
Ms Bennett agreed the proposal was contentious and welcomed healthy public debate. She said she had been congratulated by police and army personnel who strongly support the scheme.
The policy is a favourite of Prime Minister John Key, who raised it in his state of the nation speech last year, talking about the "1000 ticking time bombs" of youth offenders on the streets.
Auckland University psychologist Ian Lambie agreed boot camps alone would not work but could be effective with long-term follow-up. He said the Defence Force would need support to deal with the highest-risk youths, and more skilled clinical psychologists and social workers were needed.
"At the end of the day, we've got an inadequate workforce," he said. "There's no specialist training in child and adolescent psychology in New Zealand and it's a gap."
- The Dominion Post