The Education Ministry has revealed it is planning for mega schools for up to 4500 students.
It told RNZ its modelling indicated there could be secondary schools that size in high-growth areas by 2043.
"In these areas our modelling indicates school sizes by 2043 may approach 1000-1200 student places for a primary school, 1100-1200 student places for an intermediate school, and 3500 - 4500 student places for a secondary school," it said.
Auckland's Mount Albert Grammar School principal Patrick Drumm said his school of 3200 students would reach those figures by the end of the decade.
"The master planning we're doing here at Mount Albert Grammar is definitely for 4000," he said.
"We're growing at a 150 a year so we're going to hit those upper limits well ahead of 2043."
He estimated the school could reach 4000 within four or five years and said the school had already talked to ministry planners about growing to 4500 students.
Drumm said with good planning the school could personalise students' learning and ensure they had good relationships with their teachers and with one another, but it needed to reconsider its systems as it grew further.
"We've been looking around the world to try and find examples of big schools and how they function and what are the characteristics of them, rather than just walk blindly towards that number," he said.
"The question for me is do you just upscale another 30 percent until you get to 4000 in terms of those practices or is there a need to step back and gather expert advice around that, around how you may try to run a school at 4000."
Auckland's Rangitoto College is the only other school in New Zealand with more than 3000 students and the biggest in the country with 3250.
Its principal Patrick Gale said he did not want the school to get any bigger and the ministry would have to plan a school of 4000 very carefully.
"It's an interesting concept and I'm not sure how much research has gone into this. I'm aware that we are the largest school on a single site at least in Australasia and there are some schools in the states that may be bigger than us but it's not something that's being pushed as a model," Gale said.
"I understand the economic reasoning behind it from the ministry's point of view, but I think there's ways of planning quite carefully to ensure schools are not massive."
Gale said the ministry might want a big school to divide into junior and senior sections.
He said big schools needed clear systems for pastoral care, and could provide a lot of curriculum choices for students.
Burnside High School principal Phil Holstein said the Christchurch school was built in the 1970s as New Zealand's first super-sized school and now had 2500 students.
He said big schools had to be organised in a way that ensured students were not lost in the crowd and he urged caution over super-sized schools.
"I'd probably suggest as we did with Burnside that it's a trial first, see how it goes. I wouldn't be allowing all schools to do it at the same time."
Post Primary Teachers Association president Jack Boyle said the ministry needed to figure out if schools of 4500 were a good idea.
"There's a whole lot of work that needs to go in in the first instance to establish whether or not we should have schools of that size and if we do what sorts of things we need to have in place to make sure the learning experience for young people is what we want it to be."
The ministry said its modelling showed primary schools could reach 1200 children by 2043.
Just four primary schools had more than 900 pupils, including Finlayson Park School in Auckland.
The school's principal Shirley Maihi said it had more than 1000 pupils and 1200 was definitely too large.
"Quite frankly I think over 800 is far too many children in one space," she said.
"It's difficult when you've got a lot of younger children who seem to need more space for expansive activities - running and hopping and skipping and throwing balls," she said.
Maihi said she would prefer her school was smaller and the ministry should build more, smaller schools rather than one or two big ones.
The principal of another school of more than 900 children, Gladstone Primary in Auckland, Dave Shadbolt, said large primary schools needed sufficient space for all the children and good organisation.
He said his school was arranged into three mini-schools.
"As long as you think about how you organise the school within the school it can still function incredibly higher and as intimately as a little small school," he said.
Shadbolt said the school would finish the year with 970 pupils and he was not sure how much more it might grow.
"Possibly we'll go over 1000 in three or four years."