Māori students do better in schools that teach in a different way - but the language by itself is not enough.
Principal Chris Grinter of Rotorua Boys High School, one of 16 schools in the final phase of the programme up to 2013, credits it for helping 92 per cent of his Year 12 Māori roll gain Level 2 in the National Certificate of Educational Achievement (NCEA) last year - well above the national Māori average of 77.5 per cent.
But he says the changes took his teachers "out of their comfort zone".
"It's not about te reo as such," he says. "It's more about a learning environment where young Māori can experience success, and celebrate success, as young Māori."
The language is part of the mix. At Rotorua Boys, which has more Māori boys (605) than any other school except the Correspondence School, te reo Māori is compulsory for all students in Years 9 and 10.
But it's also about the style of teaching.
"We realised that having the teacher at the front of the classroom putting notes on the whiteboard - we can prove over many, many years that that hasn't worked for Māori boys," says Grinter.
"We had to put relationships before the curriculum."
All staff now recite their pepeha, describing their family and geographical origins.
"If you are talking about relationships with Māori students, once he hears a pepeha of a new staff member, a Māori student takes a different view of that person and the relationship starts," Grinter explains.
Teaching has become more interactive and collaborative.
"Māori students love working collaboratively, power-sharing, letting students have a greater say on when an assessment happens and what the assessment might look like."
And all teachers understand and respect not just te reo Māori but the Māori world-view.
"For example, our whole school can stand and karakia [pray] on special occasions," says Grinter.
The school has also deepened its longstanding relationship with local iwi Ngāti Whakaue, which helps fund some programmes and is involved in school events.
There is only limited data on whether the language by itself makes a difference. In 2015, 78 per cent of students from Māori-medium kura left school with at least NCEA Level 2, compared with only 62 per cent of Māori students from English-medium schools. But only 2.9 per cent of all Māori school-leavers attended Māori-medium schools, so their success doesn't prove much.
But the ministry report found that the whole suite of changes in Te Kotahitanga lifted its 16 schools' Māori students' Year 12 NCEA Level 2 achievement rates from 45 per cent in 2009 to 60 per cent in 2012 - three times the rate of improvement of other Māori students.
Similar gains were reported by many of the 94 schools in a follow-up programme Kia Eke Panuku, which was funded until last year.
But Kia Eke Panuku director Dr Mere Berryman says funding for teacher professional development has now been devolved to local "communities of learning", which are often focused on literacy and numeracy.
"We have an increasingly narrow curriculum and assessment focus rather than understanding learning as part of school-wide cultural reform," she says. "Culture and identity are being forgotten."
Te reo reaches Auckland Grammar
"Just being able to be comfortable in your own skin, it sort of sets a platform for many other things," says final-year Auckland Grammar student Nikau Reti-Beazley.
Nikau, 18, attended Māori-speaking kohanga and kura in Glen Innes and Mt Albert and chose to board at the InZone hostel to get into the Grammar zone.
But when he arrived in 2013, Auckland Grammar was one of 39 NZ secondary schools that did not teach te reo Māori at all.
Nikau has helped to change that. In his second year there, he and another boy were allowed to study te reo by correspondence.
Headmaster Tim O'Connor says this coincided with a wider curriculum review.
"Out of that process there were some suggestions that we should introduce Mandarin as a subject. When that came up, what followed was the question if we were going to introduce Mandarin, why would we not firstly introduce te reo?" he says.
"We could find no reason why we wouldn't introduce te reo."
So Mandarin was deferred, and instead last year the school hired its first te reo teacher in its 148-year history, Neitana Lobb.
Lobb teaches all Year 9 students one class a week for half a year, covering tikanga Māori and basic language.
He also teaches one full subject class in Year 10, and will offer subject classes in Year 11 next year and at all five year levels by 2020.
Nikau does his own te reo study in Lobb's Year 10 class, and helps the younger students.
"It was difficult [before]," he says. "Actually to have a staff member on site, with the resources and everything, it just makes it like a thousand times easier."