Teachers and principals are blaming the national standards in reading, writing and maths for a sudden drop in 10-year-olds' scores in an international reading test.
For the past 15 years, New Zealand's average score in the Progress in International Reading Literacy Study was static at about 530 points, but in the most recent round of testing it fell from 531 points to 523.
New Zealand's ranking in the study also fell, from 23rd to 33rd out of 50 countries.
The president of the teacher union, the Educational Institute, Lynda Stuart said the standards were to blame because they took the joy out of many classes after they were introduced in 2010.
"The creativity has actually gone and we know that creativity helps children to learn within that literacy and numeracy area."
Principals Federation president Whetu Cormick also blamed the standards for the drop.
"The profession has always been fearful that with the narrowing of the curriculum that we would see a slip," he said.
"Many would argue that when you fixate on a particular area, kids are going to switch off and this is what has happened. Children are being relentlessly pushed in reading, writing and maths."
Jessica Craig from Victoria University's school support body, Accent Learning, said the standards could well be behind the decline.
"It could be because it seems to be the only thing that's really changed," she said.
"It may be because there's just been a narrow focus on reading and kids have become more stressed about being assessed."
Dr Craig said other possibilities were socio-economic gaps, and the high incidence of bullying in New Zealand schools.
However, the director of the Woolf Fisher Research Centre at Auckland University said he wanted to see more evidence that the standards were to blame.
Professor Stuart McNaughton said the PIRLS results indicated New Zealand children were reading less non-fiction, were engaging in less high-level comprehension tasks, and fewer of them were reading for fun in their spare time.
"We have had a sense of focusing on the basic parts of reading and limiting the degree to which we've exposed children to a variety of texts and complex texts and things like that," he said.
"That may have come about because we do have a very strong view that we need to make a difference to all groups of students."
Education Minister Chris Hipkins said international evidence showed a focus on targets and standards did not work.
"One of the problems with a standardised approach is that schools and teachers are encouraged to teach to the standard and only to the standard and then when a different standard is applied, suddenly they find that actually the overall achievment is not that flash."
"A standardised approach isn't working for us and it's therefore time to look at alternatives."
Mr Hipkins said the government would give teachers more training and better programmes to improve children's reading.
The study showed socio-economic background and attendance had the biggest impacts on New Zealand children's reading ability.
It also showed New Zealand children suffer high rates of bullying and are more likely to be grouped by ability than children in all other countries bar Northern Island.