The secondary teachers' union is unhappy Labour is telling teachers how to teach reading, writing and maths.
On Monday, Labour education spokesperson Jan Tinetti announced from 2026 teachers must use government-approved methods for teaching the subjects.
The methods are part of the so-called "common practice model", which the Education Ministry had been working on since last year in an effort to improve children's literacy and numeracy.
Tinetti said making the model compulsory would ensure consistency across the country.
She said it would ensure the same principles underpinned teachers' work, and they would retain a lot of flexibility.
The model was due to be published some time in the fourth and final school term having been delayed from this term, and Education Ministry information said it would include teaching methods and phase-by-phase guidance.
Post Primary Teachers Association acting president Chris Abercrombie said the government's move was highly unusual.
"There's no other aspect of our curriculum where this is dealt with in this way so it is really unusual. We know this happens in overseas jurisdictions, but it is very unusual to be told how to teach something. What to teach, that's always there in the curriculum, but the 'how to do it' is really unusual," he said.
Abercrombie said making particular approaches to teaching compulsory would make it harder for teachers to innovate for students who needed something different.
He said the union was increasingly worried education was being politicised ahead of October's general elections.
"What we need in education is certainty. We've already got one party saying 'we're going to change the curriculum' if they come in, we've got another party saying 'we're going to do this' if it comes in, so we're really concerned about the politicisation of our national curriculum," he said.
"Taking pedagaogy [the method and practice of teaching] away from the profession and putting it in the hands of politicians is of serious concern. Doctors don't have laws about how they treat patients day to day, lawyers don't have laws about how they prosecute their clients' cases; making laws about how teachers teach is the thin edge of the wedge."
Kaiapoi North School deputy principal Felicity Fahey, who helped develop the common practice model, said it probably needed to be compulsory.
"I think there's pros and cons for it and it's a necessary thing at the moment. We want to make sure that the teachers understand the importance of this common practice model. It's not a pick and mix of do what you want. It's this is the best way the evidence is showing that we need to teach our children," she said.
Fahey said teachers would not have to search for the best ways of teaching reading, writing and maths, because the common practice model had done that research for them.
University of Otago college of education associate dean Naomi Ingram said mandating the model ensured it would get more government support.
"Mandatory's not just about all the accountability attached to being mandatory, mandatory means it's going to have really good support behind it," she said.
"They're going to throw resources at this and that will help teachers."
Ingram said the model would show teachers a pathway for teaching that would make them more confident they were doing the right thing.
"It's a roadmap for the success of ākonga," she said.
Educational Institute president Mark Potter said the union supported the model but he warned it would not work if it was too detailed and prescriptive.
"What will determine how teachers respond to this is how much it infringes on their professional autonomy. Teachers are always up for and love to see ideas and ways of teaching, they're always looking for that. But what they're not keen on, and it does not work, is being told what to do, when to do it, how to do it in their school, their classroom," he said.
Potter said he was not sure the model needed to be mandatory but schools needed more consistency in their teaching of reading, writing and maths.
Principals Federation president Leanne Otene said telling teachers how to teach was unusual, but she was not surprised.
She said teachers would support the model because they helped create it.
"We've got expertise in there and it's based on evidence and it's based on practice in our schools that we know works," she said.
"This is not national standards. We would never support anything whereby every child was to reach a certain level by a certain age."
Meanwhile, Tinetti said teacher appraisals and Education Review Office audits would check teachers and schools were using the common practice model.
She said the model would also outline what teachers had to cover at each year level of schooling.
"There will still be flexibility around how different students learn best, however what they learn and when they learn it will be much clearer."