Auckland secondary school principals say the region could be short of thousands of teachers in the next 10 years unless salaries are raised to attract new recruits.
The Auckland Secondary Schools Principals' Association (ASSPA) says in a new position paper that the region could be short of 3000 high-school teachers by 2027 and 6400 a decade later if current trends continue.
It says the top of the basic teachers' pay scale would have to jump by 36 per cent, from $78,000 now to $106,482 just to equal what it was 38 years ago in real terms, after adjusting for consumer prices.
Ministry of Education deputy secretary Craig Jones did not dispute the salary calculation, but suggested the comparison should be with average salaries over the 1980s rather than the single year of 1979.
"The drop from the eighties, if averaging the real salaries over that period, is more around 10 to 12 per cent," he said.
"After drops through the 80s there has been an increase of almost 17 per cent since 1995."
He said base salaries were not a full reflection of teachers' take home pay because there were units and other allowances teachers could earn on top of their salary.
The Post Primary Teachers Association has signalled that it may seek a pay rise this year of about 14.5 per cent and a housing allowance in areas where the median house price exceeds seven times the top of the basic teacher pay scale - likely to include Queenstown-Lakes, Auckland, Wellington City and Tauranga.
Secondary principals spokesman Richard Dykes, of Glendowie College, said principals supported the claims.
"We have got lots of cases of teachers leaving Auckland to buy a house," he said.
"They can't afford to buy a house, they can't afford to live here, they can't afford the transport costs, the cost of living.
"We have got to address that and, even with a pay increase across New Zealand, that would still leave a problem in Auckland, so we have to address that. The PPTA suggestion of a rental or housing allowance - absolutely that makes sense to ASSPA."
The principals' projections are based on Statistics NZ's medium projection for Auckland's population to increase by a third over the next 20 years, from just under 1.7 million last year to 2.2m by 2037, with a consequent need for a third more, or an extra 2350, secondary teachers.
But 21 per cent of New Zealand secondary teachers in 2015 were aged 60 or over, and the principals assume that about a tenth of those will retire each year over the next decade.
A further 24 per cent of secondary teachers are in their fifties so the projections assume that a tenth of them will retire in each year from 2027 to 2037.
At the same time, the numbers of new domestic teachers graduating from training courses has declined by 39 per cent from a recent peak of 5635 in 2012 to 3465 in 2016, according to data due to be released by the ministry today.
The projections also allow for a continuing loss rate of 38 per cent of new teachers who leave teaching within five years, and for net migration out of Auckland of 0.5 per cent of the city's teachers each year.
As well as paying teachers more, Dykes said principals wanted more training courses based in schools so that trainees could be paid a salary during their training, rather than accumulating more student debt.
"We have to make it attractive to millennials," he said.
The new ministry figures show that new teachers graduating in mid-career, aged 25-plus, have dropped by 46 per cent since 2012, while those aged under 25 have slipped by only 25 per cent.
Former Tertiary Education Minister Steven Joyce restricted student loans for part-time and older students from 2011 and imposed a four-year limit on student allowances from 2012 - measures Dykes said made it harder for people to switch into teaching when they had family commitments.
"Teaching traditionally draws in a lot of people as a second-career choice, but they are more pay-sensitive because they are in a later stage of life," he said.
Current Education Minister Chris Hipkins said the drop in teacher trainees since 2012 was "a shocking failure of planning by the previous National Government".
A spokesman said Hipkins felt it was "premature to talk about pay ahead of negotiations later this year".
He said more in-school training "could be considered as part of the workforce planning work he has started".