Mid-year figures show schools in the Auckland region had 4113 more students than at the same time last year - resulting in the fastest growth in 17 years.
Education Ministry data showed the increase was the highest in the region's 1 July roll return since 2003 and followed five years of growth of between 2600-3600 per year.
The 2020 increase occurred despite the pandemic cutting more than 1000 foreign students from the city's tally and preventing new immigrants from entering the country.
Last week RNZ revealed the ministry is moving to introduce or amend 135 enrolment schemes in Auckland so it can better manage the city's growth.
The president of the Auckland Primary Principals' Association, Stephen Lethbridge, said schools in some areas had seen growth slow or stop this year, while others had experienced no let-up in their rapid expansion.
"With the borders being closed down immigration has slowed so therefore that growth has plateaued and in other regions where it's growing it's from people moving into new developments and shifting houses," he said.
Lethbridge said primary school principals were not reporting large numbers of returning New Zealanders.
"We've noticed in our place maybe three to four families coming back from overseas," he said.
Pressure on high schools expected
The president of the Auckland Secondary Principals' Association, Steve Hargreaves, said he was surprised by the figure given that the borders had been closed since early in the year.
He said returning New Zealanders could be behind secondary schools' share of the growth.
"They must be, certainly this half of the year, attached to Kiwi families returning home. So they're probably coming out of I guess the UK, Europe, possibly people with residency coming out of Asia, or South-East Asia as well," he said.
Hargreaves said the growth figure could be at the top end of forecasts for Auckland and it would put pressure on schools.
"That's going to have some flow-on consequences for staffing and school capacity and I think that's where we probably need to be a little concerned."
He said 4000 extra students would require about 200 more teachers and 20 more classrooms.
"You can't just produce trained teachers and classrooms on the spot. There's a lead-time to all of this and that's where I think some schools might start to bulge at the seams or struggle to cover classes," Hargreaves said.
Beating 2023 forecasts
The principal of Beach Haven School, Stephanie Thompson, said her school started growing quickly 18 months ago and currently had 100 more students than at the same time last year with a further 100 possible next year.
Thompson said the school had a roll of just over 460 and she did not know where it would stop.
"We had a demographics report completed by the ministry, we are already surpassing the 2023 predictions," she said.
She said the growth was coming from new Kainga Ora and private housing developments and but for the "Covid interruptus" effect of the pandemic, it would have been worse.
"If anything, the pandemic has slowed the growth in that these developments haven't been completed yet, so in a way that's given us a wee bit of breathing space to work with the ministry to get some property," she said.
Thompson said the school had to convert a former dental clinic on its site into a classroom because of this year's growth and though it needed four new classrooms it was getting only two next year.
"They won't be here until term two so I am hopeful the Kainga Ora development will just be a little bit slower to come online because I have a rush, I literally don't have anywhere to put children," she said.
An extra 300 students in a year
The principal of Ormiston Primary School, Heath McNeil, said there was growth nearly everywhere in Auckland.
"Out of the 20 catchments across Auckland, 18 have been designated as property and roll growth hot spots," he said.
McNeil said his own school had grown by about 300 students a year in the last couple of years and looked set to repeat that figure this year.
He said the school was struggling to find space for so many children.
But not all schools were seeing runaway growth.
The principal of Balmoral School in Mount Eden, Malcolm Milner, said there was no shortage of out-of-zone students wanting to join his school's intermediate classes, but the number of new children from within the neighbourhood was unexpectedly down.
"In my new entrants Year 1 class we've seen a big drop-off in the number of enrolments," he said.
"Normally we'd be up to between 80 and 90, I think we're running round about 45 to 50 this year so that's a big drop-off."
He said the fall might be because houses in the area were selling for millions of dollars and were out of reach of most families with small children.
Whatever the cause, it was not what he had been expecting.
"If you asked me to predict a trend two years ago I'd be having this graph going up, at the moment I've got this graph sort of plateauing or going down slightly. For me, without the deep knowledge of the demographics of the area I can't predict anything. There's no trend I can see at the moment," Milner said.
The ministry's figures showed Auckland's 1 July enrolment total had grown since 2014 by almost 19,508 children - nearly as many children as went to school in all of Taranaki, and more than all of Southland's schools combined.
Its plans for Auckland included a forecast that the city's schools would grow by 60,000 students between 2018 and 2030, requiring 30 new schools and the expansion of 21 others.
Growth a bit higher than rest of NZ - Ministry
Growth for Auckland in the last year was 1.4 percent compared with 1.1 percent for the rest of the country, Ministry of Education deputy secretary Katrina Casey said.
Auckland growth was higher for secondary schools (1.78 percent) compared with primary schools (0.91 percent).
However, growth in the city's primary schools was considerably stronger than nationally (0.27 percent) while secondary school growth was lower - 1.99 percent nationally.
Casey said in a statement that short-term growth numbers were in line with the ministry's projections.
"We continually work with schools to ensure they have the space they need and are as confident as we can be that schools in high-growth areas such as Auckland have the capacity.
"We regularly monitor and evaluate factors affecting schooling provision, such as school roll data, population projections, large-scale residential developments, infrastructure projects, and the impacts of Covid-19."
The primary measures the ministry used to help schools manage growth, included putting in place or changing existing enrolment schemes and building new teaching spaces, Casey said.