As you may have suspected, your late-night-instant-messaging offspring probably aren't getting enough sleep to thrive in school. A Brown University study -- the first to enlist teachers to measure the impact of sleep loss -- recently found that cutting kids' rest decreased their attentiveness and classroom performance.

The study, which appears in the December issue of the journal Sleep, tracked 74 healthy children ages 6 to 12. During the first week, kids got their usual dose of shut-eye. In Week 2, first- and second-graders got only eight hours in bed; older kids got 61/2. Week 3 provided a luxurious minimum of 10 hours under the covers. At the end of each period, teachers rated participants on a 34-question survey. The results were clear: When kids suffered sleep loss, they had more trouble paying attention, recalling previous lessons, absorbing new material and producing the kind of work that would make Mom and Dad proud.

YAWN? Some of this might sound pretty obvious, admits lead researcher Gahan Fallone. So why did he bother? Although several studies have targeted sleep loss among teens, very few have focused on younger children. What's more, unlike previous researchers, Fallone avoided participants' self-reports, opting instead for the more reliable assessments of teachers who were blind to kids' sleep level.

WAKE-UP CALL Fallone hopes his work will set off an alarm among educators and health care practitioners. Despite frequent diagnoses of attention and learning problems, he argues, "sleep is often the elephant in the room that we're not really trained to ask about or assess." In fact, according to a National Sleep Foundation survey, more than half of parents reported that their kids' pediatricians asked no questions about sleep.

SSSSH! For parents who want to help sleep-starved kids, start by adding just 10 minutes per night and work up to the recommended 10 or 11 hours, suggests Daniel Lewin, director of behavioral sleep medicine at Children's National Medical Center. Cut the caffeine, he advises, and free the hour before bed of other stimulants, including video games, cell phones -- even homework.

-- Stacy Weiner