It’s not just lack of sleep: why pupils with an “owl” chronotype get lower grades

Cognitive performance fluctuates throughout the day. Depending on their "chronotype" some people are sharpest in the morning ("larks"), while others generally prefer the later hours of the day ("owls"). For obvious reasons, this is mirrored in our preferred sleep routines: larks get tired in the evenings earlier and, as a consequence, also wake up earlier, while owls show the opposite pattern. Your chronotype is not something that you're stuck with for the rest of your life, but it changes with age. In fact we're most likely to show an owl-like chronotype during adolescence, which might at least partly explain why teenagers often stay up late and arrive at school with eyes bloodshot thanks to a hefty sleep debt.

But if late chronotypes are so common in adolescents, why does school start so early (usually well before 9am in the UK, Netherlands and Germany)? Doesn't that mean that many students are likely to be constantly sleep-deprived and not assessed during their biological peaks? Yes, it does! In fact, there is a lot of evidence to suggest that school kids who have a late chronotype score lower grades. But besides reduced sleep time, there are several alternative explanations for why a late chronotype could be associated with lower academic performance (such as absenteeism, for instance) as explored in a new paper in Scientific Reports. The researchers, led by Giulia Zerbini at University of Groningen, say their findings might help us understand the chronotype/school grade link and how we can fix it.

The researchers collected more than 40,000 individual exam grades across multiple school subjects from 523 pupils (aged 11 to 17) at various Dutch secondary schools. They also assessed the chronotype of the students with the Munich ChronoType Questionnaire (MCTQ) which asked them several questions about their sleep habits, including what time they went to bed, fell asleep and woke on school days compared with the weekend. These data also made it possible to calculate social jetlag, which is a rough measure of the misalignment between biological and social clocks. For example, imagine you are generally not sleepy until midnight but that you have a job that means you have to be in the office from 7am: you are likely to be at risk of developing social jetlag because it will be difficult for you to get enough sleep to fit in with your schedule.

So did owls in this study get lower grades? Yes, they did. In fact, the negative association between having a late chronotype and poorer school performance was similar to the association between absenteeism from school and poorer grades! For every hour a student's chronotype ran later, grades dropped by 0.06 (on the 0-10 Dutch grading scale). Interestingly, this effect was largely independent of sleep duration, suggesting that even when owls got enough sleep, they still performed poorly compared with larks, perhaps because of their difficulty performing at their best during certain school hours. Consistent with this, they actually achieved similar grades to larks when they took the exam in the afternoon, nearer to their own optimal time of day. A similar pattern was also seen for the association between later chronotype and having an increased risk of dismissal from class, late arrival and social jetlag.

An even more interesting pattern emerged when the researchers looked at school subjects separately. A later chronotype was associated with poorer performance in science (except physics), but not in humanities/linguistic subjects (in contrast, absenteeism had universally negative associations with grades). The apparently subject-specific relevance of chronotype chimes with previous studies suggesting that chronotype and time-of-day variation in performance have the most pronounced effects in areas demanding fluid intelligence, such as mathematics.

These findings should give policy makers food for thought. For example, they reiterate the common observation that adolescents often have late chronotypes and that early school schedules do not match their needs. And it's not simply their fault for not going to bed early enough – often, their circadian rhythm is to blame just as much! It is promising that some British schools have begun trialling later start times. Even if there is no room for modification in terms of school times, at least it could be a good idea for schools to consider postponing science subjects and exams until after lunch. Of course, this won't transform every pupil into a potential Oxbridge graduate. But, at least it might make some of them feel less tired and help them perform at their best.

About the author

Helge Hasselmann studied psychology and clinical neurosciences. Since 2014, he is a PhD student in medical neurosciences at Charité University Hospital in Berlin, Germany, with a focus on understanding the role of the immune system in major depression.