Some students are being shut out of technology classes and playing fields as schools struggle to cope with bulging rolls.
Ministry of Education data obtained by the Labour Party lists 200 of the country's 2500 schools which had more students last year than their buildings were designed for.
Hamilton Boys' High School, with a roll of 144 per cent of its capacity, said it was forced to restrict numbers in technology subjects because the ministry refused to fund new facilities.
Three Manurewa primary schools, which were all among the six most overcrowded schools in Auckland, said they were coping with relocatable "prefabs" which in one case have been placed on a playing field.
"They are taking up valuable playing space," said Finlayson Park School principal Shirley Maihi. "We now only have one small rugby field to play on."
Labour education spokesman Chris Hipkins said the Government had been "woefully inadequate" at providing for population growth, especially in Auckland.
However, the data also reflects shifts in school popularity. In Papakura, while Papakura Normal School is at 93 per cent of capacity, Papakura Intermediate (formerly Mansell Senior School) is listed at only 23 per cent of capacity with a note saying, "Roll declining, achievement issues."
Intermediate principal Rebecca KauKau said this was out of date.
"We currently utilise 60 per cent of spaces and have achieved accelerated gains for priority learners," she said.
In Hamilton, Hamilton Boys' High (144 per cent) and Hamilton Girls' High (111 per cent) are both above capacity, but three of the city's four main coeducational high schools are below capacity: Melville (80 per cent), Fraser (76 per cent) and Fairfield (60 per cent).
Hamilton Boys' headmaster Susan Hassall said her school was already the biggest in the Waikato with 2200 students but would have 3000 if it accepted every boy who applied.
"That would be ludicrous," she said.
"We have a conscious strategic plan to reduce the roll by 100, which will mean we are still over capacity but we will be able to cope.
"It's a conscious decision to be over capacity because we are the only state boys' school in the Greater Waikato area."
She said it was "more of a philosophical discussion than a discussion about provision".
"Parental choice is being constrained. It's not that it's making all the schools overcrowded," she said.
But she said the school had to restrict numbers in electronics, information technology, food, metal and wood technology because it did not have enough specialist classrooms.
"We don't have enough specialist rooms because we are not allowed to grow," she said.
In contrast, all three primary schools in western Manurewa are overcrowded because of population growth. The combined rolls of Finlayson Park, Clendon Park and Rowandale have grown 25 per cent since 2010, from 1765 to 2198.
"It's mostly to do with housing, and it's to do with two or three families living in the house and in the garage and the caravan," Maihi said.
She said Finlayson Park's board had raised its own funds to buy three prefabs because "we got sick and tired of waiting for the ministry to agree to a building project".
Clendon Park deputy principal Dudley Adams said his school had put classes into every available space.
"We use our library, we use our tech suite, we have got three relocatables in, but it still means that our specialist spaces are not available for those things because we need to use them for classrooms," he said.
He said Education Ministry officials were due at the school tomorrow to discuss the school's request for a new two-storey block.
"We are hoping the ministry will build up rather than take away any more of our playground, because we have had to do that with our three relocatables," he said.
Rowandale principal Karl Vasau said the ministry had provided six temporary classrooms for his school and he hoped there might be money in tomorrow's Budget for permanent replacements.
"The Budget is tomorrow and we are praying to be on the top of the list," he said.
Education Minister Nikki Kaye said she could not speak about the Budget in advance.
"We are spending more than ever before. We have spent close to $5 billion since we have been in Government fixing leaky buildings and adding to capacity," she said.
"We do need to constantly do better."