Some Hawke's Bay pupils are not reaching the national averages for reading, writing and mathematics, the first - incomplete - snapshot of National Standards results suggests.
The data has been labelled "dangerous and misleading" by teachers and union groups.
A comprehensive Herald On Sunday survey revealed pupils at 32 local primary and intermediate schools were achieving at levels beneath those in the rest of the country.
Data released by Education Minister Hekia Parata on Friday claimed 76 per cent of pupils aged Years 1 to 8 reached or exceeded reading standards, 72 per cent for mathematics and 68 per cent for writing.
In Hawke's Bay the averages for the 32 schools who chose to reply to the survey were 66 per cent for reading, 61 for mathematics and 59 for writing.
Education sector union, NZEI, vice-president Frances Guy said the data should be read with caution.
"We're disappointed that they've been released in a form in which they will be used for league tables which will be very disruptive to education in New Zealand," she said.
"If there is an issue about not having good enough reporting on individuals then that needs to be dealt with, but standards isn't the way to do it."
A majority of local principals were at a conference in Australia and could not be reached for comment.
However, Hawke's Bay Primary Principals Association vice-president Mike Bain said there were fears the data would be used to unfairly compare schools.
The "untrustworthy" data could drive biased competition, he said.
Ms Guy said league tables used to rank schools told parents absolutely nothing about their child's progress.
"I can't see any good coming of them at all. It's all about setting up competition."
Mrs Parata said the results showed a "baseline of learner achievement" that would help those in need of extra of support.
However, opposition groups believe the data to be flawed as it not been trialled or moderated.