Professor Tim Olds, who studied the sleep patterns of more than 4000 children from across the country, said poor sleep was known to lead to memory recall problems and impair cognition. Many children in his study were "sleep deprived for up to two to three hours" overall from Monday through to Friday, he said, and this had ramifications not only on their education.

"Kids who are overweight and obese sleep less," said Professor Olds, from the University of South Australia. "And it's probably because they sleep less they have a predisposition to being overweight, and not the other way around."

Prof Olds said weight gain could be the result of these children being less active overall, as they often also had more "screen time" spent watching television or using a computer or games console.A routine of poor sleep could also cause hormonal changes that would promote weight gain, he added.

"It may be hormonal disruption," Prof Olds said.

"We know that short sleep can increase the hormones which make you very hungry and decrease the hormones which make you feel satisfied." The study took in children aged 9 - 17 and the results are published the Australian and New Zealand Journal of Public Health.

Prof Olds also pointed to recent research from Korea - a country which he said had an "extreme study culture" - and warned Australia adolescents were "moving in that direction" in terms of sleep. Korean 18 year-olds are sleeping 4.5 hours on school nights and 13.5 hours a night over the weekend.

"On Sunday, (Australian children) are in the habit of staying up late to midnight and beyond and they still have to get up to go to school," he said. "They accumulate this sleep deficit on Sundays that increases on Monday to Thursday, and they have a big catch-up on Friday and Saturday before the whole cycle begins again."

Prof Olds said concerned Australian parents should focus not on trying to get their children to sleep more, rather they should seek to make a child's sleep more consistent through the week. "The important thing is to even out the sleep they get," he said.