Education Ministry figures show Tauranga schools enrolled so many children they reached 98 percent of their official classroom capacity by the middle of last year, the highest figure of any city.
The schools had 24,876 children in July 2018, just 450 children fewer than their total shared capacity of 25,330.
Nationally, schools were at 86 percent of their capacity last year, an improvement on 2015 when the figure was 89 percent.
Wellington and Hamilton schools utilised 95 percent of their ministry-provided teaching space in the middle of last year. In Auckland, the rate was 89 percent, in Christchurch 91 percent, and in Dunedin 82 percent.
The Education Ministry said the capacity figures were based only on the classrooms that it provided and they did not necessarily mean that a particular school was overcrowded.
"The roll capacity figure indicates the number of students a school should be able to accommodate in ministry-owned teaching spaces. Roll capacity is used as a guide for planning purposes to determine which schools might require additional property," it said.
In Tauranga, the ministry had been building new schools and additional classrooms for some time and a new primary school opened in the Pyes Pa area this year.
However, president of the Western Bay of Plenty Primary Principals Association Matt Skilton said most principals were struggling to find room for their students.
"We're pretty much all experiencing the same thing and that is lack of space and constant sort of number eight, Kiwi attitude of trying to work out solutions, so, staffrooms, libraries, halls, break-out spaces, things like that being turned into classrooms."
New housing sees increase in students
Mr Skilton said a lot of new school buildings had gone into growing areas such as Papamoa, but schools in other parts of Tauranga were experiencing a new wave of growth from in-fill housing and demographic change.
"There's a lot of retirees that moved here that are now moving into the big developments which are the retirement villages and I know schools like Pillans Point, my own school Tahatai Coast School, we're experiencing a lot of the elderly moving out and families moving in," he said.
"So our zones remain the same size, there's no growth area as such, but our rolls are starting to burst because of the change in demographic."
Principal of Omokoroa Point School Vicki Knell said her school had 100 more children than its official capacity.
"We currently have 270 to 280 students, we've got another three starting in a couple of weeks. According to the ministry we have capacity for 175 students," she said.
Ms Knell said the school was currently using its library and another space for teaching, but the Education Ministry was building three new classrooms which would be ready before the end of this year.
However, she said as soon as those rooms were ready, the school would have to ask for more rooms because hundreds of new houses were being built nearby and the school would grow further.
"We've got 500 sections on the other side of the railway bridge which goes to the other Omokoroa school and about 300 that we know of that are being developed that will be put online by the council."
Principal of Papamoa College Steve Lindsey said his school was opened in 2011 for 1050 students but it now had 1426 and did not have enough classrooms.
"Currently we have classroom spaces that are in our lobby, in our theatre. We deck it out so that it's really useful in terms of the learning and the teaching environment. Some of the spaces are quite good to teach in, but they haven't been designed especially for that."
Mr Lindsey said the ministry was working with the school on further development and the plan was to expand the school so it could take 2000 students.
"We know about the numbers, we basically will increase by 100 students a year, that's what we're working to hence we've got the stage three and the stage four in terms of a campus development programme that we're working on with the ministry," he said.