A national study of primary school children has found a fall in performance in writing for some eight-year-olds but next to no change in reading.

The National Monitoring Study of Student Achievement run by the University of Otago and the Council for Educational Research covered 4000 children in Year 4 and Year 8 last year.

The study has been running since 2012 and Council for Educational Research chief researcher Charles Darr said the lack of change in achievement from previous years was the main finding.

He said the exception was Year 4 students in writing.

"In writing we see the scores go down, but they don't really go down for our Maori and Pacific students, it's the high-decile schools and boys in high-decile school particularly I guess as well, that have shown the drop that's been big enough to bring our population score down slightly," he said.

Darr said the lack of movement in literacy scores could be seen as surprising given the amount of attention schools had given to literacy in recent years.

Principals Federation president Perry Rush said the results were not what schools would have been expecting.

"It really is disappointing, particularly as we have worked very hard in schools with a very strong emphasis on the core, on doing better in reading and writing and mathematics," he said.

"Despite that very strong emphasis that's come through from government and in policy, we're just not seeing the gains."

Rush said it was time for schools to try new approaches to teaching reading and writing instead of persevering with more of the same.

He said the decline in writing scores for Year 4 students was "quite significant" for some groups of students could be down to increased use of technology.

"You would have to ask the question whether they are all indicators of high technology use, not just at school but also at home and the impact that is having on young people's literacy devlopment," Rush said.

The study also showed the percentage of students achieving at the level expected of their age group fell, sometimes significantly, between Year 4 and Year 8.

In reading, 63 percent of Year 4s and 56 percent of Year 8s achieved at the expected level, while in writing 63 percent of Year 4s reached the level expected of them, but the figure for Year 8s was 35 percent.

The National Monitoring Study of Student Achievement had recorded similar gaps for most subjects.

Victoria University associate dean of education Michael Johnston said schools needed more guidance on the best ways of teaching.

"We have to look to the Ministry of Education for better guidance to teachers on what the most effective methods of teaching literacy are, and also to my colleagues in the teacher training institutions to use those," he said.

Dr Johnston said the evidence suggested schools needed to make more use of phonics-based approaches to teaching reading.

Meanwhile, Darr said the study found a strong correlation between reading at home and doing well at school.

"Year 8 students who read for more than five hours a week were scoring well above students who weren't getting that reading done," he said.

"The fact that the effect seems to get bigger between Year 4 and Year 8 suggests that doing that reading and having that interest and getting that opportunity at home to extend your reading is really having an impact on your achievement."