A new report says schools are trying hard with te reo Māori but their successes are "fragile" - often depending on a single Māori teacher and liable to collapse if that person leaves.
The report by the NZ Council for Educational Research calls for a much stronger commitment to the language, including making it part of the core curriculum, more Māori-language schools and a plan to train more Māori-language teachers.
"Overall, the findings indicate that successes were fragile," it says.
"In some schools, one strong individual drove the reo Māori focus, and the school became vulnerable if that person left."
It also found that Government support for the language was "inconsistent". Efforts such as scholarships for Māori-language teacher trainees have not been matched by giving te reo the same status as other core subjects such as English and maths.
Lead author Dr Maraea Hunia said the council proposed the report to the Ministry of Education, which funded it, to look at how to stop the numbers learning in te reo declining as students got older.
"In 2014, of those who attended Māori-medium early childhood education, only 49 per cent started school in a Māori-medium setting." the report says.
"Of ākonga [students] who were in Māori-medium settings in Year 6, only 41 per cent of ākonga were still there in Year 11."
A 2011 Waitangi Tribunal report found that the numbers of Māori students learning for at least three hours a week in te reo Māori peaked at 27,127, or 16.9 per cent of all Māori schoolchildren, in 2004, falling to 25,349 (15.2 per cent) in 2009.
Those numbers have grown again to 29,012 last year (15.1 per cent of all Māori schoolchildren), including a jump in kura kaupapa Māori and kura-a-iwi [tribal schools] from 4.4 per cent in 2009 to 5.7 per cent of all Māori schoolchildren.
Hunia said there were still not enough Māori-language kura [schools] for all families to access them.
"Parents told us in the study that they found it very difficult to access te reo Māori for their students," she said.
"Their responses varied from driving more than an hour every morning to get their children to reo Māori schooling, to another parent who didn't have the resources to be able to move their kids physically but worked really hard within the local school to develop a Māori programme."
The report found that successful schools established Māori-speaking "domains" such as school marae, Māori-speaking teachers and activities such as kapa haka where speaking Māori was accepted. One English-language school put kapa haka as well as te reo into its core curriculum.
"They just sort of figured, 'Actually kapa haka is a vehicle,'" a staff member is quoted as saying. The principal "pulled it from after school and lunchtime and put it smack bang in the curriculum."
The report says a national move to make te reo part of the core curriculum "would send an important message to all schools about teaching te reo".
Hunia said that could not happen overnight because of a desperate shortage of reo Māori teachers.
"It's a little bit of chicken and egg," she said.
"The language is endangered, and we need to put a stake in the ground at some stage and find the resources and the pathway to develop the teachers over a period of time.
"There is a lot of anecdotal evidence in the media that is showing that the tide has turned and the time is right, for people's interest in te reo Māori is much bigger than it was even 12 months ago."
The Ministry of Education's chief adviser for Te Ao Māori, Dr Wayne Ngata, welcomed the report's findings.
"We are committed to improving the provision of te reo Māori in and across all education provision – and to increasing the supply of te reo Māori teachers," he said.
He said this year's Budget included $1.1 million this year and $11.4m over the next three years for Te Ahu o te reo Māori, a package of initiatives to lift capability for delivering quality te reo Māori education.
The ministry is holding regional wānanga for the public "to help shape the future of Māori education".