New Zealand's 10-year-olds have recorded a statistically-insignificant drop in performance in a major international reading test.

Their average score of 521 in the 2020/21 Progress in International Reading Literacy Study, was two points lower than the previous round of testing in 2016.

About 400,000 children in 57 countries and eight territories participated in the study in 2020, 2021 and 2022.

New Zealand tested its cohort at the end of 2020, the first year of the pandemic, while some other countries delayed testing by a year or tested their cohort at the start of their following year of schooling.

Singapore, which tested its children in English, had the highest average score at 587 points.

Considering only countries that tested 10-year-olds at the end of their year of schooling, New Zealand's score was 20th-equal with Spain.

Internationally, children from richer families recorded significantly higher scores on average than children from poorer backgrounds. The difference in average scores was 86 points and in New Zealand 84 points.

The Education Ministry says the PIRLS data has not yet been analysed to understand what factors have the strongest influence on reading achievement.

It says past testing shows good reading performance is linked to factors including early childhood education, parental engagement in early literacy activities, and having a high sense of belonging at school.

"The impact of self confidence and not being absent both have a stronger relationship with achievement than students' liking of reading; having access to books also means children are likely to read recreationally and be more confident," says the ministry.

The ministry says the previous PIRLS tests showed that there are more similarities than differences in how teachers in English-language countries taught reading.

The PIRLS data says 38 per cent of New Zealand children say they very much like reading and, like other countries, girls sre more likely to enjoy reading than boys.

-John Gerritsen/RNZ.