The number of school children in Auckland has grown at the upper limit of official forecasts this year and some schools are struggling to find enough classrooms and teachers, principals say.
The Education Ministry said provisional figures indicated the number of five to 17-year-olds in Auckland had grown by fractionally less than Statistics New Zealand's high-growth forecast of 3455 children in 2017-18.
It said most of the increase had occurred in the city's primary schools.
Auckland Primary Principals' Association president Helen Varney said some schools were growing a lot faster than expected this year.
"It's happened much quicker than expected, it's happened with a certain age group, so five-year-olds, much much higher numbers than expected, and it's come at a time when it's really hard to staff your schools," she said.
Mrs Varney said a lot of the increase was happening in the number of five-year-olds starting school this year.
Her own school normally had two new entrant classes at this time of the year, but it already had four and was planning a fifth.
Mrs Varney said it was harder to predict how many school-age children might be living in a particular area because more families were living together in a single home, sometimes for financial reasons but often because it was their preference to live together.
"Rental costs can be one of the factors, but other factors are mainly because they're keen to live with their families and they've got the support there for their children while they work," she said.
The principal of Albany Primary School, Maree Bathurst, said her school had 784 children compared to 707 at the same time last year and she expected the roll to reach 810 by the end of the year.
"Our next class will have to go in the library so we have actually no extra spaces at all. We're currently using a room that is less than ideal for a new entrant class but that is what our Education Ministry deem our capacity is so we're actually over capacity now," she said.
Ms Bathurst said the school had expected a lot of new enrolments because of new developments in the area including six apartment blocks, but it was hard for the Education Ministry to plan for growth.
"For example there's a subdivision in our zone which five years ago could have had 600 townhouses on it. It took a long time for that development to be approved by council and then there were construction problems so that growth could have had a huge impact on our school and the three local schools, but as it turned out it was very much a progressive subdivision."
At the other end of Auckland, Manurewa South School principal Tone Kolose said his roll had jumped from 320 children last year to more than 380, and it was still growing.
"We were surprised that the school's roll had grown dramatically, we weren't expecting the 20 percent increase of students. We are kind of expecting to hit the 400 mark, maybe 410 by the end of the year," he said.
Mr Kolose said the increase had forced the school to use half its library as a classroom and he expected it would have use the other half of that building and the school's hall for teaching space.
About 30 or 40 children were coming to the school from other neighbourhoods, but even with an enrolment zone the growth was unlikely to stop because other factors were driving more people into the area, he said.
"We're noticing that more families are moving in with families, so we have bigger numbers of people living in the same houses," he said.
In addition, there were new state house developments and more people buying homes in the area, Mr Kolose said.
The Education Ministry's deputy secretary sector enablement and support, Katrina Casey, said the Auckland school network grew by 8 percent or 19,500 students in the past 10 years, reaching a high of 275,465 students last year.
"The region is growing faster and at a more sustained rate than ever before and we expect over the next decade it will continue to grow at the fastest rate since 2001," Ms Casey said.
"We could see between 30,000 and 60,000 more school-age students in the network by 2030. We are working to meet this projected growth in a range of ways including optimising the current network, expanding current schools and building new schools."
Ms Casey said the ministry was working on an Auckland growth plan and a national network plan for growth to 2030, which would go to the government later this year.
She said since the 2014 government Budget the ministry had been allocated funding to provide an additional 25,000 student places in Auckland, of which 9300 had been completed and a further 3000 were expected in the next 12 months.