Primary principals are worried the Education Review Office is focusing too narrowly on children's results in reading, writing and maths when it reviews schools.
The office has written to all schools advising them that from the start of this year its reviews will explicity use schools' results and compare them with local and national averages.
Principals say the review office is putting too much emphasis on what they call dodgy national standards data.
They say it could encourage schools to focus too narrowly on reading, writing and maths and neglect science, the arts and other aspects of children's development.
They and their union, the Educational Institute, warn that schools might cheat in order to get good reviews.
The institute's national secretary, Paul Goulter, says national standards results are not reliable.
"There is no evidence at all that the New Zealand public or the sector at large believe and have any confidence in national standards data. It continues to be as (Prime Minister) John Key said ropey data, and then to move to having schools evaluated on the basis of ropey data is just absurd."
But the Education Review Office says schools should not worry, and the main difference is that the office will contact them before it visits to discuss their students' results.