Most teenagers have felt it: the groggy Monday morning after a weekend of late nights and lazy wake-ups. The gap between weekend and weekday sleep schedules has a scientific name: social jetlag and new research from Spain shows it may come with a real academic cost. A study published in the European Journal of Pediatrics found that each additional hour of social jetlag was linked to 19 to 25 percent lower odds of earning higher grades across every subject tested from math to foreign language.
The research, part of the Eating Healthy and Daily Life Activities (EHDLA) study, surveyed 788 adolescents aged 12 to 17 in the Valle de Ricote region of southeastern Spain. What makes this population especially interesting is that Spain as a whole operates on what researchers call structural circadian misalignment. Mealtimes run late, social schedules extend well past dark, and the school day starts early despite a biological clock that runs behind the clock on the wall. In other words, these teenagers face a built-in tension between when their bodies want to sleep and when society expects them to be awake.
Social jetlag is calculated as the absolute difference between a person’s usual weekend bedtime and their usual weekday bedtime. If a teen crashes at 10 p.m. on weekdays but stays up until 1 a.m. on weekends, that is a three-hour social jetlag. About half of the adolescents in this study reported social jetlag of two hours or more.
What they found
Using ordinal regression models adjusted for age, sex, socioeconomic status, BMI, and overall sleep duration, the researchers found a clear and consistent pattern. For every one-hour increase in social jetlag, the odds of achieving a higher grade point average dropped by 24 percent (odds ratio 0.76, 95 percent CI 0.68 to 0.85, p less than 0.01). The effect held across individual subjects as well: language grades (OR 0.80), math (OR 0.81), and foreign language (OR 0.75) all showed statistically significant associations. A PISA-type composite score combining language, math, and science grades showed a 24 percent reduction per hour (OR 0.76, 95 percent CI 0.66 to 0.88).
The numbers translate into a real-world pattern. A teenager who shifts their bedtime by two hours on weekends shows roughly 40 percent lower odds of receiving higher grades than a peer whose weekend and weekday bedtimes stay within an hour of each other. But the relationship is not a simple straight line. When the researchers categorized social jetlag into mild (one to two hours) and severe (more than two hours), they found that only the severe group showed a consistent link to poorer performance. Mild social jetlag was not statistically different from minimal social jetlag (less than one hour). This suggests a threshold effect: a little mismatch may be manageable, but once the gap exceeds about two hours, academic performance starts to suffer.
Why it matters
Adolescence is a period of profound biological change in the circadian system. During puberty, the body’s internal clock naturally shifts later, a phenomenon known as a delayed sleep phase. Teenagers become wired to fall asleep later and wake up later, yet most school systems require them to be at their desks by 8 or 8:30 a.m. The result is chronic sleep debt that many try to repay on weekends, widening the gap between weekday and weekend schedules.
This study is the first to examine social jetlag and academic performance in a region with structural circadian misalignment. In most sleep research, the population’s baseline schedule is assumed to be reasonably aligned with the solar day. Spain is different. The country operates on Central European Time despite sitting geographically close to the Greenwich meridian, meaning the sun peaks well after noon on the clock. Combined with late mealtimes, lunch at 2 or 3 p.m., dinner at 9 or 10 p.m., and a cultural preference for evening socializing, the result is a population whose entire daily rhythm is shifted later compared to their light-dark cycle. For adolescents already predisposed to late schedules, this structural misalignment may amplify the effects of social jetlag.
The findings also add weight to the growing argument for later school start times. Several school districts around the world have experimented with pushing the first bell to 8:30 a.m. or later, with positive results in attendance, engagement, and even test scores. This study provides direct evidence that the mismatch between a teen’s internal clock and their early school schedule, not lack of total sleep but the specific pattern of shifting bedtimes between weekdays and weekends, may be a distinct and measurable factor in how well they perform.
Limits
The study has important limitations. First, its cross-sectional design means it can show association but not causation. It is possible that students who struggle academically develop irregular sleep patterns, rather than the other way around, or that a third factor such as screen time, extracurricular workload, or family environment drives both. Second, bedtimes were self-reported rather than measured objectively with actigraphy or wrist-worn devices. Teenagers may not be perfectly accurate in recalling when they actually fall asleep. Third, the sample was drawn from a single region in southeastern Spain, which limits how far the results can be generalized to other populations with different cultural schedules and school timings. Fourth, although the models adjusted for key confounders like socioeconomic status and total sleep duration, residual confounding cannot be ruled out.
Bottom line
Severe social jetlag, a gap of more than two hours between weekend and weekday bedtimes, was consistently linked to lower academic performance in a large sample of Spanish adolescents. The findings suggest that aligning school schedules more closely with adolescent circadian biology, particularly in regions where the social clock already runs late, could help reduce the academic toll of this mismatch.
Source
Sánchez-Charcopa LA, et al. Social jetlag and academic performance in adolescents: insights from a region with structural circadian misalignment. European Journal of Pediatrics (2026). PMID: 42470595. DOI: 10.1007/s00431-026-07250-5.