In one of the most comprehensive studies to date examining teenage sleep patterns and high school start times, it's been revealed that later starts increased sleep duration and improved overall attendance and grades.

Our circadian rhythms dominate when our body wants us to eat, sleep and wake. Studies have shown that the onset of puberty dramatically alters an adolescent's circadian cycle, keeping them up at night and pushing them to sleep later in the morning.

"Research to date has shown that the circadian rhythms of adolescents are simply fundamentally different from those of adults and children," explains lead author on the new research, Gideon Dunster.

Early school start times have long been a source of controversy, with many suggesting we need to push the commencement of school back later into the morning as early starts could be significantly disrupting healthy teenage sleep patterns. A striking 85 percent of high schools in the United States have a start time earlier than 8.30am, and the average is 7.59am. For several years now the American Academy of Pediatrics has recommended middle and high schools start later than 8.30am.

The new research set out to clearly measure the effect of school start times on sleep patterns by closely studying teens at two Seattle high schools. In 2016 Seattle announced it would push middle and high school start times from 7.50am to 8.45am. This offered researchers a great opportunity to investigate conditions at two schools before and after the change.

Instead of relying on conventional self-reported sleep patterns, the researchers deployed wrist activity monitors to track light and activity levels. The first group of 92 students were tracked for two weeks before the change to the school start time. A second group of 88 students, from the same two schools, were tracked for two weeks seven months after the start time had shifted to 8.45am. The results were incredibly clear, with the students displaying an average increase of 34 minutes of sleep each night.

"This study shows a significant improvement in the sleep duration of students — all by delaying school start times so that they're more in line with the natural wake-up times of adolescents," says senior and corresponding author, Horacio de la Iglesia. "Thirty-four minutes of extra sleep each night is a huge impact to see from a single intervention."

Other improvements were also tracked by the study, including a 4.5 percent average increase in grades following the start time shift. The researchers are cautious in attributing a causal connection between the higher grades and the increased sleep, however, it is noted that it's reasonable to hypothesize better sleep can improve academic performance.

While it is becoming increasingly clear that earlier school start times may not be ideally tailored to the biological needs of teenagers, changing those start times is proving to be a bit more complicated that scientists would hope.

A recent bill in California, set to prohibit middle and high schools in the state from starting earlier than 8.30am, was ultimately rejected after a divisive debate suggested the change would be too demanding for everyone, from parents with inflexible work schedules to those teens with pre-established post-schoolday activities. So, what is more important in the long run? Is adhering to our teenager's biological imperatives and significantly altering our overall day-to-day patterns too much to change?

"School start time has serious implications for how students learn and perform in their education," says de la Iglesia. "Adolescents are on one schedule. The question is: What schedule will their schools be on?"

The study was published in the journal Science Advances.