A better alignment between chronotype and school timing is associated with lower grade retention in adolescents

The study investigates whether adolescents’ academic success is influenced by chronotype alone (chronotype effect) or by the alignment between chronotype and school timing (synchrony effect), or both. Adolescents tend to have later chronotypes while secondary schools often start early, creating misalignment linked to sleep loss and poorer outcomes. Prior evidence suggests early chronotypes perform better, particularly in morning classes, but earlier studies lacked random assignment to school timing and often omitted evening schedules, leaving open whether effects reflect intrinsic chronotype differences or time-of-day alignment. The authors articulate three scenarios: performance driven solely by synchrony (better alignment yields higher grades), solely by chronotype (earlier types do better), or by both. They extend prior cross-sectional work with a longitudinal design to test how school timing and chronotype affect academic performance and grade retention across adolescence. They hypothesize that (1) later school timings align better with adolescents’ internal time and improve performance, (2) both chronotype and synchrony effects modulate performance, and (3) even controlling for grades, later chronotypes in morning schedules will show higher odds of grade retention, with weaker effects in later timings.

The paper reviews evidence that chronotype varies across individuals with genetic and environmental determinants and can be reliably assessed by the Munich Chronotype Questionnaire (MCTQ) via MSFsc, correlating with behavioral and physiological rhythms. Adolescence is marked by delayed chronotype, often conflicting with early school start times, contributing to sleep deprivation, social jetlag, and health/cognitive impairments. Delaying school start times tends to improve mood, wellbeing, and sometimes academic performance, though findings are not universally conclusive. Studies comparing morning vs afternoon cohorts often show early types perform better in morning classes, with mixed effects by subject (stronger in math/science than language). However, prior work is limited by lack of random assignment to shifts and absence of evening schedules, confounding by preferences and baseline differences, preventing clean separation of chronotype vs synchrony effects.

Design: Longitudinal study at a selective secondary school in Buenos Aires, Argentina, with three randomly assigned school timings maintained throughout secondary school: morning (07:45–12:05), afternoon (12:40–17:00), evening (17:20–21:40). Data collected in June 2015 (1st year; age ~13–14) and July 2019 (5th year; age ~17–18). Participants: For performance analyses, 259 students who had complete data in both years and maintained their original timing (50.97% female; 1st year mean age 13.49±0.33; 5th year 17.58±0.33). For grade retention analyses, 407 1st-year students with complete baseline data (49.88% female). Students are highly selected for entry, making voluntary school changes unlikely; non-reach of 5th year within four years was treated as grade retention. Measures: Chronotype via MCTQ (MSFsc; hours), higher values indicate later chronotype. Academic performance: official yearly grades (1–10) per subject, two general and two integrative grades per year; passing requires each integrative exam ≥4 and overall average ≥6.5. Subjects considered during assigned timing; core analyses focus on math and native language (Spanish); other subjects aggregated as “other.” Grade retention coded binary: 1 if did not reach 5th year by 2019, 0 otherwise. Procedure: Questionnaires administered during usual class hours; grades and rosters obtained from school records at year-end. Students were randomly assigned to timing by lottery at start of secondary school and retained that timing. Statistical analysis: Academic performance modeled with linear mixed-effects models: fixed effects of MSFsc (numeric), school timing (factor: morning, afternoon, evening), age/year (1st, 5th), school subject (math, language, other), their interactions, and gender as covariate. Random effects: student ID, classroom (1–30), and type of grade (general vs integrative). P-values via lmerTest. Grade retention modeled via logistic regression. Model selection by AIC; base model included MSFsc, math grade, language grade, and MSFsc × school timing. The most parsimonious model included MSFsc, math and language grades, and interactions: MSFsc × school timing (synchrony), MSFsc × math grade, and language grade × school timing. Odds ratios (OR) computed from model slopes; for grades, OR represent odds of retention per 1-point decrease. Ethical approval obtained from Universidad Nacional de Quilmes IRB; participation voluntary under Argentine regulations.

- Synchrony effect on mean performance by timing and age: In 1st year, math performance was higher in the afternoon than evening (t=3.018, P=0.007, Cohen’s d=0.411). Language tended to be higher in afternoon/evening vs morning but was not significant. In 5th year, evening students outperformed morning and afternoon in math (evening vs morning: t=−3.432, P=0.002, d=−0.468; evening vs afternoon: t=−2.908, P=0.01, d=−0.396); language showed no timing differences. - Chronotype and synchrony effects on performance: Mixed-effects analysis showed main effects of chronotype (later MSFsc → lower grades) and subject, with interactions indicating modulation by age, subject, and school timing. At 1st year: later chronotype predicted lower math performance in morning (β=−0.200, 95% CI −0.343 to −0.057, P=0.006) and lower language in evening (β=−0.185, 95% CI −0.354 to −0.017, P=0.031); no significant associations in afternoon. At 5th year: math slopes were negative across all timings, strongest in morning (morning β=−0.535 per 1-h later MSFsc, 95% CI −0.708 to −0.363, P<0.0001; afternoon β=−0.250, 95% CI −0.404 to −0.096, P=0.002; evening β=−0.238, 95% CI −0.404 to −0.072, P=0.005). Morning slope was significantly steeper than afternoon and evening, evidencing synchrony moderating the chronotype effect. - Grade retention determinants: The selected logistic model showed lower 1st-year grades predict higher odds of retention (math: F1,406=51.156, P<0.0001; language: F1,406=18.006, P<0.0001). Chronotype main effect was not significant (F1,406=3.050, P=0.081), but the interaction MSFsc × school timing was significant (F1,405=7.260, P=0.027), indicating a synchrony effect on retention. - Odds ratios: For students with math grades 1-point below average, a 1-hour later chronotype increased odds of grade retention in the morning (OR=1.656, 95% CI 1.121–2.447) but not in afternoon (OR=1.168, 0.815–1.676) or evening (OR=0.949, 0.728–1.237). For average or above-average math grades, MSFsc ORs were not significantly different from 1 across timings. A 1-point decrease in language grade increased odds of retention more in morning (OR=3.106, 1.700–5.464) than evening (OR=1.553, 1.088–2.217). The MSFsc × math grade interaction was marginal (β=−0.173, P=0.050), suggesting greater vulnerability to poorer math grades among later chronotypes.

Findings indicate that academic success in adolescence is shaped by both intrinsic chronotype differences and alignment between chronotype and school timing. Performance benefits from later schedules increase with age, consistent with adolescents’ progressively later chronotypes. Math appears more sensitive than language to both chronotype and synchrony, aligning with evidence that fluid intelligence tasks are more time-of-day dependent. The synchrony effect mitigates, but does not eliminate, the disadvantage of later chronotypes; even in evening schedules, earlier chronotypes can retain a performance edge. Beyond grades, synchrony significantly affects grade retention: later chronotypes face higher retention risk specifically in morning schedules, even after accounting for initial grades, whereas this association is absent in later schedules. The study highlights that focusing solely on grades may underestimate timing-related disadvantages, since higher morning retention can selectively remove lower-performing students from later-year grade analyses. The interplay of chronotype, timing, and subject suggests mechanisms including sleep, alertness, and possibly motivation contribute to outcomes.

The study demonstrates that aligning school timing with adolescents’ chronotypes improves academic outcomes: later schedules are associated with better performance, and misalignment in morning schedules increases retention risk for later chronotypes. Both chronotype and synchrony effects jointly influence performance—especially in math—and synchrony uniquely predicts grade retention. Policy implications include delaying school start times, assigning later chronotypes to later shifts when feasible, and scheduling math later in the day, particularly for morning cohorts. Future research should employ objective sleep measures (e.g., actigraphy), evaluate teacher-related timing factors, conduct translational and local policy trials, and further disentangle causal pathways linking sleep, motivation, and academic trajectories.

- Grades were teacher-assigned, with teachers unblinded and varying across courses; teacher chronotype and timing were not measured and could introduce bias, though the large number of teachers and courses likely dilutes systematic effects. - Chronotype was self-reported via questionnaire; objective measures (e.g., actigraphy) were not used. - The study is correlational; causal inferences are limited despite random assignment to school timing. - Grade retention classification may conflate repeating a year with school transfer or dropout; authors argue such cases are unlikely given school selectivity, but cannot be fully excluded. - Performance analyses included only students with data in both years and stable timing (n=259), potentially underrepresenting those more likely to be retained, which can bias observed performance effects.