Chinese students aren't the only ones who have a sleep loss problem. In Australia, teenagers are also missing out on, on average, one hour's sleep every night during the school week. Organized activities and homework push bedtimes later, the first large-scale Australian study of children's sleeping habits has revealed  . Their sleep deprivation   is enough to cause "serious drop-offs in school performance, attention and memory", and governments should consider later or flexible school start times, said the study's leader, Tim Olds. ks5u His survey, of more than 4,000 children aged 9 to 18, found those who slept least did not watch more television but spent their time socializing   with family or friends or listening to music. "Almost all children get up at 7 or 7:15 -- they have to get to school on time," said Olds. He favors a later start over an earlier finish because he believes organized sports and activities would still consume the latter end of the day. Olds' research also establishes lack of sleep as a cause of weight gain in children, and a possible source of future problems with depression, anxiety and increased susceptibility   to illness. It was already known that overweight children sleep less, but Professor Olds found sleep duration  was strongly linked to weight across the full range of body sizes. The thinnest children sleep 20 minutes more than the  _ . This showed being overweight had no specific effect on sleep patterns, and it was more likely that shorter sleep times stimulate   appetite and make kids hungry. The US National Sleep Foundation says teenagers aged 13 to 18 need eight to nine hours' sleep a night. Younger school-aged kids need 9 to 11 hours. On that basis, Professor Olds said, half of Australian children are under-sleeping on weekdays and a quarter on weekends. The Australian students surveyed don't sleep enough because they spend more time on the following EXCEPT   _  .
organized activities and homework communication with friends and family watching television programs enjoying music