The Principals' Federation is worried about a big change to the way the schools watchdog, the Education Review Office (ERO), monitors schools.
Reviewers will visit schools as often as several times a year, rather than once every few years.
The president of the Principals' Federation, Perry Rush, said the new system would not work unless the reviewers were more supportive.
"The sort of mindset that ERO has had in the past have meant that reviews can be incredibly corrosive on a school's confidence and on a principal's wellbeing, and if reviewers are going to be in schools much more frequently it's absolutely critical that they have a significantly changed mindset," he said.
"If they are unable to do that then this new model will fail, because principals will not let reviewers into their schools."
He said reviewers focused too much on reading, writing and maths, and some were out of touch with the realities of classroom teaching.
Rush said some principals could see promise in the new method of reviewing, but others were worried by the prospect of repeated visits.
The principal of Ōtorohanga College, Traci Liddall, said her school was preparing for an ERO review visit next month, which she understood would incorporate some elements of the new system.
She said ERO reviews could be useful, especially for schools that need improvement, and she could see how more frequent review visits might be good.
"Tentatively I think it would be a good idea," she said.
"Relationships are everything. The current model they get a snapshot of where you're at, at that point in time, which isn't necessarily a reflection of the school as a whole. Having a relationship with an ERO person over time potentially means that they can see the big picture.
"It does depend how well the principal gets on with the ERO person or not, that could have a significant impact. It also depends on whether they can move away from just looking at data."
The principal of Northcross Intermediate in Auckland, Jonathon Tredray, was one of the principals who advised the review office on its new approach.
He said he was confident it would be an improvement, because reviewers would have a much better understanding of the schools they were monitoring.
He said the intention was also to provide schools with more support so they could improve.
The chief review officer Nicholas Pole said most schools would not be reviewed more frequently, but they would have more frequent contact with review officers.
Pole said the frequency of visits would depend on each school's particular situation.
"We've been piloting at the moment in a group of schools who have been really struggling in their context, and we have been going back very regularly. Whereas other schools that are doing really well - it might be just a very light engagement," he said.
He said review officers might visit a school every year, but only for a catch-up, rather than a full review.
Asked about the Principals' Federations criticism of "corrosive" reviews, Pole said: "The new approach is clearly based on collaboration, and we want the senior leadership team in the school, members of the board, members of the community, to be absolutely with us through the review process."
He said the office would help schools focus on continuous improvement and on the things that had the most impact on their work.
ERO's statement of intent said it had concerns about 8 percent of schools, but that schools were generally particularly poor at evaluating their own work.
"Over time we increasingly want to shift schools to being much stronger in their own self-review," Pole said.