Lack of sleep could be linked to childhood obesity, the author of a new study says.
And the loss of 30 minutes' sleep could have serious consequences, the University of South Australia's Dr Jim Dollman said on Tuesday.
"That's the difference in sleep duration between overweight and normal weight children, according to a recent study overseas," he told ABC radio.
"So it may well be that 30-minute reduction is contributing to the increase in prevalence of overweight in children."
The problem was self-reinforcing, he said, because overweight children often suffered from sleep problems.
Children aged 10 to 15 years are sleeping at least 30 minutes less every night compared with a generation ago, Dr Dollman has found.
Increased part-time working hours, mobile phones, computer usage and television watching are to blame, with adolescents no longer adhering to "lights out", he says.
NSW Parents and Citizens Federation president Dianne Giblin said the problem of tired teenagers was not new.
The parents' group suggests flexible school hours could be a better solution to tired and inattentive teenagers than banning mobile phones and computers from the bedroom.
Ms Giblin counselled greater understanding of the trials of adolescence and said allowances should be made.
Schools in the US had successfully experimented with later starting times, she said.
"By starting school later in the day you will get a much more productive young man in the classroom."
The UniSA study, published on Monday, compared the results of two surveys - the 1985 Australian Schools Health and Fitness Survey and the 2004 SA Physical Activity Survey - which involved about 500 children from the same eight schools.
Dr Dollman said increasingly complicated households, part-time work and the abundance of modern gadgets in children's bedrooms had led to the change in sleeping patterns.
But Ms Giblin said every generation of children had new toys to play with.
"Us as young people ourselves had other sorts of technology that kept us up at late hours of the night," Ms Giblin told ABC radio.
"I don't think by battling with your child that's going to have the effect that we desire."