New Zealand schoolchildren are among the most sleep-deprived in the world - and technology is flagged as a possible factor.
Researchers found Kiwi children were second only to the United States in a comparison of sleep deprivation.
They say lack of sleep plays a significant role in lowering the achievement of schoolchildren.
The international comparison, carried out by Boston College, found 69 per cent of 9 and 10-year-olds and 62 per cent of 13 and 14-year-olds who were tested in maths were identified by their teachers as being adversely affected by not enough sleep.
That number is above the international average of 47 per cent and 57 per cent respectively. In literacy tests, 69 per cent of Kiwi 9 and 10-year-olds were without enough sleep.
NZ Principals' Federation President Philip Harding said teachers saw sleepy children in class "all the time".
Parents needed to realise the home environment was crucial to how their child performed in school, he said. "Some of our parents are powerless in the face of kids that don't want to go to bed, or kids who connive to stay up.
"Who's in charge? I think modern parenting demands parents to think about who is the boss, who knows best, and what should be happening, and then to make that happen."
Mr Harding said that while adults could react differently to sleep-deprivation, becoming irritable or listless, for children it generally manifested as a behavioural problem.
"It's not just the negative effect of not being primed for learning, they can be actively more troublesome."
The study did not examine why children were lacking sleep, however Mr Harding said the proliferation of technology such as computers and smartphones was partly to blame.
"Light [from electronic screens] suppresses the development of melatonin, which helps you go to sleep ... today kids and adults sit and watch television on a big flat screen, and they've got computers ... they are doing the exact opposite of what they need to be doing to get to sleep."
The findings are part of global education rankings known as the Trends in International Mathematics and Science Study (TIMSS) and Progress in International Reading Literacy Study (PIRLS).
The studies are based on maths, science and reading tests taken by more than 900,000 children in more than 50 countries. Results were studied with interview responses from teachers and parents about sleep habits. Researchers acknowledged sleep deprivation was not the only indicator of academic success. High-performing countries such as Finland suffer relatively high levels of sleep deprivation.
However, Chad Minnich, of the TIMSS and PIRLS International Study Centre, said a lack of sleep nonetheless had a significant impact on learning. He said children in classrooms where instruction was limited due to pupils' lack of sleep have, on average, lower achievement in mathematics, science and reading.
Saudi Arabia, Australia and England were other countries with a high proportion of children lacking sleep.
Children who get the most sleep were from countries including Azerbaijan, Kazakhstan, Portugal, Japan and Malta.
Among world's worst
• Kiwi kids are among the most sleep-deprived in the world
• The studies are based on maths, science and reading tests taken by 900,000 children in 50 countries
• It was found that 69 per cent of 9 and 10-year-olds and 62 per cent of 13 and 14-year-olds who were tested in maths were adversely affected by not enough sleep.
• Results were studied alongside interview responses from their teachers and parents about their sleep habits.