The ACT Party wants to reverse a law change made under the previous National-led Government that widened the jurisdiction of the youth justice system to low-risk 17-year-olds.
Leader David Seymour said his party supported the legislation in 2016 as part of its confidence and supply arrangement with National, but he believes it hasn't had the desired effect.
"We were told the worst offenders would still go through the adult system, and somehow youth crime would reduce," Seymour said on Sunday. "Those things have turned out to be wrong, and we must now have the courage to correct a mistake."
Former National Justice Minister Amy Adams said in 2016 that while Youth Court was "not a soft option", it was "effective at reducing crime and holding young offenders to account".
But Seymour said that three years on from the change coming into effect - the change didn't begin until 2019 - there hadn't been a change in offending rates.
"Relative to 18 and 19-year-old offenders, 14 to 17-year-olds were half as likely to offend in 2018/19, and they are still around half as likely to offend in 2022/23," Seymour said.
"Specifically, in the 2018/19 year, 14 to 16-year-olds were 52 percent as likely to be proceeded against by Police as 18 and 19-year-olds. Last year, 2021/22, 14 to 17-year-olds were 52 percent as likely to be proceeded against by Police.
"One of two things has happened. 17-year-olds started committing half as much crime to fit into their new age category, or 17-year-olds kept committing crime but got proceeded against half as often under the Youth Justice system. In theory it could be either, but which one sounds more plausible?"
The latest Youth Justice data shows that while young people remain about half as likely to offend as 18 and 19-year-olds, the overall number of youth offenders has dropped significantly since 2011/12 despite the inclusion of 17-year-olds.
In 2011/12, the number of young offenders was 11,557, compared to 5765 in 2021/22.
ACT would amend the relevant legislation so any 17-year-old who allegedly committed any offence would have their case heard in either a district or high court.
"It would not mean that all 17-year-olds who commit minor sentences end up in jail, as the courts still have a range of sentencing options available to them," ACT's policy document said.
"If young people under the age of 18 are sent to prison, they will be within a youth unit (or a segregated adult unit if a youth unit is not available), rather than housed within the general prison population."
Seymour said 17-year-olds were old enough to face adult justice.
"It’s an age when young people should understand that consequences come from breaking the law and that they will be held accountable for doing so."
The ACT leader also said that youth offenders are being housed in "inappropriate" Oranga Tamariki facilities which have recently been the scenes of chaos.
"Oranga Tamariki’s job is to protect vulnerable children, not to house young men who are well on the way to becoming hardened criminals," Seymour said.
"By placing these young men into the adult justice system where they belong, ACT will remove a burden from Oranga Tamariki which will help them focus on their core role. It will also ensure that 17-year-old youth offenders can be kept somewhere secure, where they can no longer harm others, and where they can get the appropriate rehabilitation."
Oranga Tamariki youth justice residences have come under significant scrutiny recently.
This week, Newshub revealed footage of an MMA-style fight occurring at the Korowai Manaaki facility in south Auckland, the same place where five teenagers recently escaped onto the roof. A number of staff have been stood down.
Former Police Commissioner Mike Bush has recently been brought in to review the Oranga Tamariki youth justice facilities after it was revealed two staff members were removed from the Government department residences after allegations of inappropriate and sexual behaviour surfaced.