The Education Review Office (ERO) has concerns about student learning and achievement at one in five of the country's schools.
Education groups like the Principals Federation and the Secondary Principals Association say the figure is so high it raises questions about the entire school system.
Chief review officer Graham Stoop told Parliament's Education and Science Select Committee this week that 20% of schools will be reviewed every one or two years.
That frequency signals concerns about a school - and those concerns, says ERO's national manager of evaluation services, Diana Anderson - are not trivial.
She says they might involve teaching, assessment or school-wide systems for improving learning.
Schools reviewed less often 'misusing status'
Last year the office changed the frequency of school inspections in order to focus on those most in need of help. About 70% of schools are on a three-year review cycle, while 10% are reviewed every four or five years.
The longer cycles have been introduced for schools that the ERO has no concerns about and that meet a range of measures for good practice.
But the president of the Secondary Principals Association, Patrick Walsh, says that some schools are misusing that status to promote themselves and that schools on shorter review cycles might be equally good academically.
Ms Anderson says it's up to schools how they use the review reports.
Weaknesses in system perceived
About half the schools being reviewed every one or two years have improvement plans in place, but the Principals Federation and the Secondary Principals Association say that the 20% figure indicates weaknesses in the school system and that the Government should look at what needs changing.
Mr Walsh says ERO could identify national trends in schools that the Ministry of Education could then investigate.
The head of the primary teachers union reckons struggling schools need help faster. New Zealand Educational Institute president Frances Nelson says such schools need to be identified and helped more quickly.