The government has been warned its moves on youth crime could lead to teenagers glorifying the "young serious offender" category it is setting up.
The coalition government is going ahead with legislative changes to enable the Youth Court to declare an offender a "YSO".
But official advice warned this approach was complicated, inflexible and would only deal with a few persistent offenders a year - between 10 and 30 out of several hundred.
"A legislative YSO category may result in delayed court proceedings; young people glorifying the 'YSO' label (this occurred in Australia); and restricting or delaying the ability of the police and courts to access any strengthened powers to a narrow 'YSO cohort'," warned a single-page advisory from Oranga Tamariki (OT), which has been proactively released.
This would also require "significant and complicated legislative changes", and fixed criteria set in law for declaring a YSO - based on the risk of future reoffending - would likely be "too narrow and miss a high-risk cohort of young people".
Officials instead recommended taking a "non-legislative" approach, by defining a YSO based on offending history and assessments of why a teenager kept on offending.
"Quality criminogenic assessments would provide a much more accurate indication of future reoffending risk", they said.
RNZ has asked the Prime Minister and Children's Minister why this advice was rejected, with a commitment in January to taking the legislative route.
The legislation they have proposed would let the police apply for a YSO declaration on teens between 14 and 17 who have committed two offences punishable by 10 years or more in prison, and were likely to reoffend.
A YSO teen could be ordered to undergo a boot-camp course of three months in a secure youth justice centre, and nine months rehab in the community. Currently, without such a law, teens can not be sentenced to boot camp, and have the option not to stay - one has already left the pilot boot camp in Palmerston North.
A YSO would allow greater use of electronic and judicial monitoring of a teenager, and access to more intensive rehabilitation services.
The government has said the moves are key to cutting youth reoffending by 15 percent.
Budget 2024 put $37 million into establishing the legislation and boot camp operations.
OT said in its latest public commentary that the government's move "would "unlock a range of new powers for police and the Youth Court".
But its earlier behind-the-scenes advisory pointed out that more than 90 percent of young offenders were dealt with outside the courts - while a YSO could only be used where an offence had been proven in court.
The documents released by Oranga Tamariki also showed that Finance Minister Nicola Willis got the budget for setting up and running the pilot cut by a third - from $6m to $4m - primarily by switching to a reliance on internal OT staffing "instead of recruiting a new external workforce as originally planned".
Officials had noted how an earlier version of boot camps - called MACs - that ran from 2010-16 had 25 OT and 10 Defence Force staff - "insufficient to produce good outcomes".
The documents also reveal deep-seated concerns at the Defence Force about being involved, beyond giving some training to OT staff.
The government for months talked about the NZDF's involvement, saying it was heavily involved.
But in January, the Defence Force had already told officials it could not host a boot camp on a defence base, where teens might get "access to dangerous equipment" and had concerns "about the suitability of its staff given the high needs of this cohort and that approximately 80 percent have confirmed or suspected mental health or disability-related diagnosis".
Children's Minister Karen Chhour still wanted to push on with assessing if the Defence Force considered it had "sufficient skilled personnel" to deliver the pilots and if it could deliver a permanent military academy programme, briefings showed.
At that stage, officials wanted two pilots - one in September 2024 and a second next year, with an eight-week residential component, compared to three months in the current pilot - and two permanent locations to "enable more frequent intakes to occur".
One big failing of the MAC was it was based in Christchurch, but most of the teenagers came from the North Island, so follow-up afterwards was poor and let them down.