Being underprepared and not getting enough sleep are reasons why New Zealand school children are lagging behind their international counterparts, research has found.
Maths is a particular problem area, with more than two-thirds of primary school children lacking the necessary background knowledge for lessons - and their teachers admitting a lack of confidence to teach the subject.
The findings are contained in a Ministry of Education analysis of global education rankings known as the Trends in International Mathematics and Science Study (TIMSS) and Progress in International Reading Literacy Study (PIRLS).
Seventy-six per cent of Year 5 students (aged 9 and 10) were identified by teachers as lacking some or a lot of the necessary background knowledge for maths lessons.
NZ Principals' Federation president Phil Harding said that was a common gripe of teachers at all levels, however maths, in particular, was a subject under the spotlight.
The Education Review Office was calling for urgent action to improve maths teaching in primary and intermediate schools.
"Asian countries are particularly good at raising student achievement in mathematics ... they do it in a very structured way.
"The New Zealand model is based more on language and problem solving. But if that's not translating into improved performance, then we have to rethink some of that," Mr Harding said.
The new reports looked at the results from the international tests, published last December, within the context of responses from teachers, parents and students, as well as other background information.
Fewer middle primary teachers felt well prepared to teach maths compared with their peers overseas, the reports found, and fewer expressed high levels of confidence to teach the subject.
Only 57 per cent of Year 5 students had teachers who said they were very well prepared to teach adding and subtracting with decimals.
Sleep deprivation is also an issue, with 69 per cent of Year 5 students identified by their teachers as adversely affected by not enough sleep.
Kiwi children were second only to the United States in a comparison of sleep deprivation.
Diane Muller, of the Sleep/Wake Research Centre at Massey University, said her research had found parents of 6- to 8-year-olds overestimated the amount of sleep their children got.
"On school nights, parents overestimated sleep by an average of 37 minutes, and on non-school nights by an average of 58 minutes compared with the actigraphically measured sleep."
Ms Muller said that unlike in adults, sleepiness in children might appear as hyperactivity, poor impulse control and inattention, which could affect school performance.
She said it was advisable for kids not to use computers or tablets before bedtime, as they were stimulating and the light could potentially interfere with the circadian body clock.