Education Minister Hekia Parata says the results show New Zealand has stabilised on a global scale, but more work needs to be done.

Kiwi students have improved their ranking in maths, science and reading on an international scale, but have failed to improve their average scores across those three subjects.

New Zealand has gone from 18th to 12th in science, from 23rd to 21st in mathematics, and from 13th to 10th in reading, according to a report released by the Organisation for Economic Co-operation and Development (OECD) on Tuesday night.

About 4500 New Zealand 15-year-olds from 183 schools sat the 2015 Programme for International Student Assessment (Pisa) test, which is done every three years.

ROB YOUNG/FAIRFAX NZ The international report shows New Zealand has moved up the world education rankings, but without improving its scores.

Figures also showed that, across all rankings, New Zealand's average scores had gone down since 2012.

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Education Minister Hekia Parata celebrated the results. "We can always improve, but what is very good about 2015 is we have arrested the fall, and have stabilised and consolidated," she said.

"We're are comfortably in the top half of OECD, we're in the top 10 out of 70 [countries] for reading, 12th for science and we've made very small progress in maths, but even so, at 21, we're very comfortably in the top half.

"There is still a lot of work to be done, but these results tell me we are doing the right things."

New Zealand's rise in the rankings was largely because countries previously ranked above it declined, Craig Jones, deputy secretary for evidence, data and knowledge said.

Labour education spokesman Chris Hipkins said the figures showed student performance was dropping across all three subject areas.

"The biggest drop was between 2009 and 2012, but it's continued to decline," he said.

The average score for New Zealand kids had gone from 516 to 513 in science, from 512 to 509 in reading, and from 500 to 495 in maths between 2012 and 2015.

He said the rankings were nonsense, and ultimately a way to look at how other countries were doing.

"We are primarily competing against ourselves. What it shows is we are getting worse year on year ... there isn't anything positive in these numbers."

The report also showed that the gap between advantaged and disadvantaged students in New Zealand was larger compared with other OECD countries, Jones said.

But big gaps between high and low socio-economic students did not mean a poorer background always resulted in poor achievement.

"If you're from a low socio-economic background, lots of kids perform really well compared to other OECD countries," he said.

New Zealand Educational Institute president Louise Green said the figures showed New Zealand had one of the worst equity gaps in the world.

"The OECD have done in-depth studies in this area, and they link underachieving with poverty," she said.

"The number of kids in New Zealand bracketed in the low-performing area has increased, and in a time when the Government has said we need to reduce the gap and improve equity.

"We need to put more resources into schools within areas of high poverty so those kids get opportunities to succeed, and those kids with special learning needs.

"And we also need better professional learning and development for teachers so they're confident they can deliver up-to-date and relevant lessons to their students."

Half a million 15-year-olds in 72 countries, made up of 35 OECD countries and 37 partner countries and economies, sat the Pisa test in 2015.