In classrooms across America, many students may be a little bit "out of it" because they didn't sleep well last night.

So says a recent survey in the Journal of School Health. About 200 fifth-grade students were polled, and most said they didn't get enough sleep at least a few nights per week.

That's no surprise to their teachers, who reported yawns, misbehavior, and sleep-problem complaints from their students. But some parents didn't seem to know that their kids were secretly staying up past bedtime or tossing and turning, the study suggests.

The Goal: 10-11 Hours Per Night

Ideally, elementary school children should get 10-11 hours of sleep per night, say the researchers, who included Denise Amschler, PhD, a professor of physiology and health science at Ball State University.

"Good sleep is as important as daily exercise and proper nutrition," says Amschler's study.

Most of the students she surveyed said they didn't get enough sleep. One in four said they slept too little five to seven times per week, and 39 percent said they didn't get enough sleep two to four nights per week.

Typical Bedtimes

On school nights, most said they went to bed at 9 or 9:30 p.m. However, bedtimes of 10 p.m. or later were common.

That makes getting 10 or 11 hours of sleep difficult since 83 percent of kids were up by 7 a.m.

The study doesn't link up bedtimes and rising times for each child. But if a student went to bed at 10 p.m., for example, and rose at 6:30 a.m., that would be 8.5 hours of sleep -- far short of the mark.

That sleep deficit could cast a shadow over the child's day. Just like adults, the mood and performance of kids might suffer with sleep deprivation.

Bedtime Clashes With Parents Common

Nearly half of the students said they argued with their parents at bedtime.

Many kids disobeyed their assigned bedtime, secretly staying up later than their parents realized. About 30 percent said they stayed up later than their parents knew five to seven nights per week. Another 32 percent admitted doing so two to four times per week.

Kids with TVs and computers in their bedrooms might be tempted to stay up late, say the researchers. However, their study didn't ask about bedroom TVs and computers.

Restless Nights Not Unusual

Some kids had trouble falling asleep. Only 27 percent said they could regularly fall asleep within 20 minutes.

Pain was a common reason for losing sleep, keeping nearly half of the students up at least two nights a week.

No wonder, then, that over 80 percent of the students said they felt sleepy during the day at least twice a week.

Classroom Impact

The kids' teachers said about a third of the students yawned during the day, almost a fifth were hyperactive, and around one in six students complained about sleep.

The teachers said one in eight students struggled to stay awake. Few of those students actually fell asleep in class, disrupted class with their sleepiness, or had major discipline problems, according to the teachers.

By Miranda Hitti, reviewed by Michael W. Smith, MD

SOURCES: Amschler, D. Journal of School Health, February 2005; vol 75: pp 50-56. News release, Ball State University.