Hans Henrik Sievertsen from the Danish National Centre for Social Research in Copenhagen and his team have looked at 2 million standardised test scores from Danish children aged between 8 and 15. Starting from 8 am, for every hour later that a test was taken, scores declined by an amount equivalent to the effect of missing 10 days of school. Children who were performing worse at school seemed most affected by the time they sat the exam.
The team thinks the difference is down to cognitive fatigue. If a test was taken just after a 20 or 30 minute break, scores improved by as much as if the children had taken it 2 hours earlier.
How children’s mental resources get recharged is unclear. “I’m very interested in what’s going on in these breaks,” says Sievertsen. “Is it because they have something to eat, or fresh air? If we know that, we can maybe speculate why some children are more affected than others.”
Time is against you
Sievertsen doesn’t advocate changing school schedules. Instead, he suggests that tests should always be taken at the same time in different schools, possibly after a break. “Another solution would be to calculate ways to adjust test scores according to test time and whether you had a break,” he says.
In the US, some national tests used to select college applications start at 8 am.
But school isn’t all about exams. Many studies have found that teenagers tend to benefit from a school day that starts later, and some countries are debating whether school days should start later to suit teenagers’ body clocks.
“The medical sleep researchers who have been specifically studying teenagers around the world have found that teens tend to become more alert as the day progresses,” says Kyla Wahlstrom, at the University of Minnesota in Minneapolis. However, this latest study didn’t detect any differences at different ages.
The hour of the day doesn’t just influence the performance of children. Judges are much more likely to offer a favourable ruling at the start of the day or just after lunch, and doctors are more likely to prescribe antibiotics for respiratory infections as the day wears on.