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A working paper for the National Bureau for Economic Research in the United States said New Zealand's place in the PISA league tables would improve if more students applied themselves and answered all the questions in the two-hour test.
The study said students in some countries did not care about the PISA test because it did not count for anything apart from a certain amount of national pride.
The working paper said 27% of New Zealand students who sat the 2015 test rushed through the computer-based exam or left questions unanswered, compared with just 17% in top-ranked Singapore. In Australia the figure was 22.5%, in the UK 17.5%, and in Finland 16%.
About 5000 New Zealand 15- and 16-year-olds were scheduled to sit the latest edition of the three-yearly test between 23 July and 14 September.
Michael Johnston, senior lecturer in education at Victoria University, said the study's assumption that New Zealand students were not trying hard enough if they left questions unanswered might not be correct.
Dr Johnston said it might be a by-product of the NCEA assessment system.
"In NCEA students can opt out of certain standards and certain aspects of assessment and still get credits for what they do, whereas in most other countries that's not true," he said.
"So if our students are used to that way of thinking about assessment then perhaps that's why they show up as being more likely to be what the researchers call non-serious."
Dr Johnston said NCEA could be improved, but it should not be changed merely in order to improve the country's PISA scores.
"That would be a perverse thing to do," he said.
Auckland Secondary Principals Association president Richard Dykes said schools did take the tests seriously, but they did not prepare their students for them.
"We don't train our students for them, nor should we. PISA is not a high-stakes exam for students so therefore we would not ask our students to study towards it, we don't get our students to do practice tests for it. If you want to give the system integrity you shouldn't be doing that."
Mr Dykes said it appeared some countries were preparing their students for the tests and that made international comparisons unfair.
"There's a bit of a growing cynicism amongst some educationalists in New Zealand because anecdotally, and that's all it is, there are possibly other countries that are doing just that, they're gaming the system by drilling their students for it and you've got to ask if they're doing that - are we really comparing apples with apples."
New Zealand's PISA scores have fallen steadily, reaching their lowest point ever in the last round of testing in 2015 with a score of 513 points for science, placing it behind 11 other countries, 509 for reading placing it 10th, and 495 for maths, putting it in 21st place.
University of Auckland education professor Stuart McNaughton said the ongoing decline was worrying, but he hoped lessons had been learned from previous results.
"We learned quite a lot from the last PISA round about where the points of system performance should change. One of those was at the top end, that is our highest-scoring students, and making sure that our focus on excellence and cognitively complex performance isn't compromised in any way," he said.
"However, I do think that a number of changes in the system levers, the way our policies impact on schools, need to change before we will see major changes in those trends."
Professor McNaughton said that included ensuring schools in poor communities got more resources and the very best teachers so they could raise achievement among the most disadvantaged students.
"If there is another decline it would tell us that we still haven't got the system levers right," he said.