Kids in elementary school need at least nine hours of sleep a night - something too few of them these days are getting.
Lack of sleep is affecting kids in the classroom, says Dr Carl Hunt, director of the government's National Centre on Sleep Disorders Research.
"As you talk to teachers … they tell us that children being sleepy in school is very common," Hunt says. "And studies have shown that kids who don't get enough sleep don't do well in school, [and] they have problems both behaviourally and emotionally."
Kids ages 5 to 11 should get at least nine hours of sleep a night - a number associated with good health, good performance and fewer accidents - although not everyone believes it's that absolute.
"The number nine is not a magic number," says Suzan Jaffe, who specialises in treating insomnia in children and adults in Florida. "Some kids who are 11 may only need 8½ hours, while some kids who are 7 may need 11 hours. It depends on the kid."
"But generally," Jaffe agrees, "primary school kids are not getting enough sleep."
Hunt says that "a good night's sleep is as important to good health as a healthy diet, for everyone of all ages."
Sleep deprivation can result in fatigue, concentration difficulty, easy frustration and problems controlling impulses and emotions.
But little attention has been paid to the problems of sleep in children, Hunt says. "As doctors we haven't had access to a lot of information about sleep deprivation in children," he says. "Sleep is not something that has been emphasised in health-care training."
Kids have jampacked lives nowadays, Jaffe says.
"Not only do they have a full day at school, but unlike us, who went to school and took math and reading, kids today are also learning second languages, computers and sciences," she says. "Then they go home, [and] they have an hour of homework. And then they want time on the computer, and they want to watch two hours of television and they want to play with their Game Boys. And on top of that, they have to find time to eat, or have a bath or talk to mommy and daddy."
But it's essential that kids learn good sleep habits early in life, she says.
"The sleep habits that are developed early in life are the sleep habits we have as adults," Jaffe explains. "It's like eating habits."
Not getting enough sleep also can affect growth or make kids susceptible to illness, she says.
"Before puberty, sleep deprivation can cause a change in hormones since growth hormones are produced at night," she says. "And lack of sleep leads to poor behavior, poor attention skills and bad listening skills."
And sometimes, Jaffe says, lack of sleep is misinterpreted as attention deficit disorder.
"The behaviour kids use to keep themselves awake may look to the unsophisticated eye as [attention deficit] or some sort of behavioural or discipline problem," she says. "What's really going on is the kid is simply exhausted."
(Liesel Powell, Health24)