Sunlight, Later School Start Times Benefit Students

Sunlight, Later School Start Times Benefit Students

Jennifer HeisselStudents who received more sunlight before school did better academically – especially in math – than those who were exposed to less sunlight, according to new Northwestern University research.

The study, published online in the Journal of Human Resources, is one of the first to look at the importance of school start times as well as sunlight on a child’s academic performance, said study author Jennifer Heissel, of Northwestern’s School of Education and Social Policy.

“Sunlight matters, especially for adolescents,” said Heissel, a postdoctoral candidate in human development and social policy. “School districts can improve average performance by moving classes earlier for younger children and later for older children.”

The study adds a new factor -- sunlight exposure -- to the debate over school start times, which have been changing as evidence mounts that adolescent brains need more sleep.

Sleep patterns are partially regulated by signals from the sun, which vary across time zones.

Heissel and co-author Samuel Norris, a graduate student in the department of economics at Northwestern, examined the hours of sunlight available before school in the Central/Eastern time zone boundary in Florida’s panhandle.  

In the Eastern time zone, children generally get less sunlight in the morning and more sunlight at night, which naturally pushes sleep cycles later.

The students living in the Central time zone receive bright sunlight in the early morning and less after school, which should mean better sleep and morning alertness.

The researchers tracked students who moved from the Central time zone to the Eastern time zone and found that having less sunlight before school was associated with poorer academic outcomes, especially in math.

Moving the start times one hour later, relative to the sunrise, increased test scores for teens in math and reading. The effect was larger for older students in both subjects.

Heissel and Norris also found the effects on test scores were larger for math, and do not appear to be driven by improvements in test-taking alone. Instead, later start times supported learning throughout the school year.

Since teens naturally stay awake later than younger children, those in the Eastern time zone are getting a double hit: Less sunlight in the morning and a body that wants to stay awake later, Heissel said.

“The estimated effect sizes for an extra hour of sunlight before school are much larger for adolescents,” she said.

The shift in effect happens two years earlier in girls than in boys, which makes sense, said Heissel, because girls tend to go through puberty a couple years before boys.  

“One of the most compelling parts of the research is that the sleep changes are driven by puberty and not necessarily a behavioral effect,” Heissel said. “That makes it harder for people to say a child should just get to bed earlier. It’s harder to do that when your body is telling you to do something different.”

By Julie Deardorff
Last Modified: 5/30/17