A report from the OECD's Programme for International Student Assessment (PISA) shows New Zealand's 15-year-olds spend more time on the internet than their peers in all countries except Denmark, Sweden and Chile.

It says results from the 2018 PISA tests show New Zealand teens were spending 42 hours per week online, well above the OECD average of 35 hours per week and 22 hours higher than in 2012 - equal with Costa Rica for the biggest increase of any of the 79 nations and economies in the study.

The report also found New Zealand was one of just five countries where use of digital devices at school was associated with better performance in reading.

The PISA tests have shown a slow decline in New Zealand 15-year-olds' achievement in reading, science and maths during the past 18 years.

An education professor at the University of Auckland and chief scientific adviser to the Ministry of Education, Professor Stuart McNaughton says there's not enough evidence to show increased screen time is to blame for falling achievement in the PISA tests and other measures.

"It's a bit of a long bow at the moment. We can't link causally, easily, the increase in device use and use of the internet and the dropping reading achievement scores but it is certainly possible that there is a relationship," he says.

McNaughton says it's clear that, apart from extreme high use, the amount of time spent online is not as important as what young people are doing while online.

"The issue around the relationship or potential relationship with achievement over years is whether or not the digital device usage, internet, social media, is somehow in conflict with or undermining our reading and writing activities, school-related or non-school-related," he says.

McNaughton says the report shows that reading longer texts is associated with better reading scores, and the challenge is to find ways of ensuring young people are reading them.

The report says the time teachers spent using digital devices in class had a negative impact on students' reading performance in most countries, but New Zealand is one of five that bucked that trend.

"The association between time spent using digital devices and positive performance is only positive in Australia, Denmark, Korea, New Zealand, and the United States," the report says.

It said New Zealand 15-year-olds are using digital devices in class for about 84 minutes per week - less than Denmark, but more than the other three nations - and the associated increase in reading scores is higher than in the other countries.

It says browsing the internet for school work is the digital activity most strongly related to reading performance and New Zealand is among countries where half or more of students did that every day or almost every day.

Some activities, especially playing simulations, had a negative impact on students' reading performance.

File photo/RNZ.

The principal of Albany Senior High School, Claire Amos, says she suspects New Zealand's good performance is the result of deliberate efforts to find good ways to use technology to support literacy.

"We have very proactively looked at how we can use these technologies to enhance literacy teaching and learning and I think we've front-footed that," she says.

Amos says she's not surprised that New Zealand teens are spending more time online than their peers in most other countries, because schools had encouraged students to use their devices and there is high internet coverage across New Zealand homes.

But she said she was concerned that the report showed a strong digital divide.

"We still have a tail end of young people who aren't doing as well in lower socio-economic areas," she says.

"That just doubles down on the need for us to really get on and close that digital divide in our schools because, where are young people have access to technology, where our teachers are confident in using that technology, it's clearly having a positive impact on their literacy learning and their literacy acquisition and skills."

The study found that, internationally, teenagers who read printed books were better readers than those who read digital books or no books at all.

It also found that teens at schools that expected them to read texts longer than 100 pages were better readers. New Zealand had the 12th highest proportion of students at such schools.

The report says, across the OECD, 54 per cent of students said they were taught at school how to recognise if information was biased.

New Zealand's teens scored well on questions testing their ability to discern opinion from fact, and were good at navigating the internet to find information from multiple sources.

It says 90 per cent of New Zealand students had access to a computer they could use for schoolwork and a link to the internet at home, though the figure ranged from about 80 percent at lower-decile schools to more than 95 per cent at higher-decile.

It said enjoyment of reading had fallen in New Zealand and in many other countries and enjoyment was closely linked to high performance in reading. New Zealand teens were reading for enjoyment for about 3.5 hours a week, slightly less than in 2009, but the same as in 2000 and the same as the OECD average.

The report found, internationally and in New Zealand, that when students were reading online, fewer were spending much time reading emails than in 2009, but more were reading online chats (about 90 percent, up from less than 60 per cent in 2009), reading online news, searching for information on a particular topic, participating in online discussion groups, and searching for practical information.

-RNZ/John Gerritsen.