For the US city, it was a small revolution: for a good two years, teaching at all 18 public high schools and most middleschools in Seattle is no longer beginning at ten to eight, but at a quarter to nine - with a startling effect.
Not only the parents had to be convinced of this innovation. The timetable of the school buses has also been changed. And from the sports club to the music school, employees had to adjust to new start times in the afternoon - all in the hope that the teens appear fitter in the morning to class.
The change has paid off, the students are more alert. That's what scientists from the University of Washington and the Salk Institute for Biological Studies found out from a small group of students. Their results have been published in the science journal "Science Advances".
34 minutes more sleep
"The study shows a significant improvement in the sleep duration of students," said study author Horacio de la Iglesia. Accordingly, the teenagers sleep much longer on average, the median increased by 34 minutes. This means that half of the students sleep at least seven hours and 24 minutes every night during the weekday shift. Before the change, the median was six hours and fifty minutes a night.
For the study, the researchers compared the sleep behavior of around 90 students from two high schools for 14 days before and after the transition to school. The data was collected with fitness bracelets worn by study participants on the wrist. They recorded subjects' activity and lighting conditions every 15 seconds.
Accordingly, the bedtime of most of the students has not moved backward by the later beginning of school. The ringing of the alarm clock but already. As a result, they got more sleep.
The inner clock of teens tick differently
"Previous research has shown that adolescents' basic clock is fundamentally different from that of adults and children," said co-author Gideon Dunster. The changed getting-up time rather corresponded to the rhythm of teenagers.
While the time of falling asleep is determined biologically, the wake-up time is socially conditioned, says Dunster. If the adolescents are woken up too early, it will have a negative effect on their health and well-being, said the doctoral student in biology. Her attention span also suffers from lack of sleep.
However, the problem of young people's lack of sleep due to the later start of school in Seattle is not completely solved. Scientists recommend eight to ten hours of sleep for the age group. Of these, the subjects from this study are still removed.