(NEWS) Flexible school start times & teenagers' sleep: Swiss study shows +44 minutes of sleep per night

Imagine if your teenager could decide for themselves when school started in the morning – and thereby sleep almost 45 minutes longer, get better grades, and feel less exhausted. What sounds like a dream was investigated by researchers at the University of Zurich and the Children's Hospital Zurich in a large-scale, long-term study. The result is clear: 95% of the students took advantage of the option to start an average of 38 minutes later – and benefited from an additional 44 minutes of sleep per weekday, less fatigue, and improved academic performance (Journal of Adolescent Health, 2026). The study shows that sleep is not a luxury, but a crucial factor for health and academic success. But how exactly does it work? And what role does the body's internal clock play? This article explains the findings – in a practical and evidence-based way.

What the study shows

In the Swiss study, researchers observed 2,641 students (aged 12–20) at two schools with flexible morning start times for over a year . The students could choose between two start times – and the result was impressive:

• 95% chose the later start time (an average of 38 minutes later).

• +44 minutes of sleep per night on weekdays (actigraphy measurement).

• +26 minutes of sleep per night throughout the entire week (including weekends).

• Less tiredness: subjective exhaustion decreased by 14% (Epworth Sleepiness Scale).

• Improved grades: The average grade in core subjects rose by 3.5% (0.2 points on a 6-point scale).

• No negative effect on afternoon activities (sports, hobbies remained stable).

Mechanism: Why does a later school start time help?

The explanation lies in the circadian biology of teenagers: During puberty, their internal clock shifts later (circadian phase delay) – teenagers get tired later in the evening and need longer to wake up in the morning. Early school start times (e.g., 7:30 a.m.) often fall right in the middle of their biological night.

• Melatonin breakdown: In teenagers, melatonin (sleep hormone) is broken down more slowly in the morning → later natural waking up.

• Chronic sleep deprivation: Early starts lead to social jetlag (discrepancy between biological and social time).

• Cognitive performance: Lack of sleep impairs the prefrontal cortex → poorer concentration, memory, impulse control.

• Mental health: Chronic sleep deprivation increases the risk of anxiety, depression, and mood swings.

• Flexibility as a solution: A later start synchronizes school hours with the biological clock → more natural sleep-wake pattern.

Dosage & application: What does that mean in practice?

The study shows that even small adjustments can have big effects. Here are the most important practical tips:

• Optimal start time for teenagers to start school: between 8:30 and 9:00 a.m. (instead of 7:30–8:00 a.m.).

• Flexibility is key: Having a choice (e.g., two start times) increases acceptance and individual adaptation.

• Onset of effect: positive effects (sleep, fatigue) become apparent within 1–2 weeks.

• Long-term effects: stable for over 1 year (no habituation effects → adolescents did not revert to old patterns).

• For home use: Even without flexible school hours, consistent sleep hygiene helps (fixed bedtimes, no blue light before sleeping, dark room).

For whom is a later start to school particularly suitable?

• Teenagers (12–20 years): circadian phase shift during puberty makes a later start biologically advantageous.

• Students with chronic sleep deprivation benefit the most (responder rate in study: ~95%).

• Adolescents with learning difficulties: improved cognitive performance through sufficient sleep.

• Families with commuting parents: flexible hours reduce morning stress.

• Not suitable: no contraindications identified (athletes and recreational users also benefited without disadvantages).

Comparison: Flexible vs. fixed school start times

The study shows clear advantages of the flexible model compared to rigid school hours:

• Sleep duration: flexible +44 min, fixed +0 min (meta-analyses show: count every 10 min).

• Fatigue: flexible −14%, fixed ±0%.

• School performance: flexible +3.5%, fixed ±0%.

• Acceptance: flexible, 95% usage; fixed, often resistance from students and parents.

• Organizational hurdles: flexible requires replanning, fixed is simpler – but: one-time changeover, long-term advantages.

• Combined with sleep hygiene: flexible start + good sleep habits = maximum effect.

Side effects & contraindications

• No adverse health effects: no increased risk of adverse effects identified.

• Potential organizational challenges: transportation, family planning (but: solvable through lead time and communication).

• No disadvantage for afternoon activities: sports and hobbies remained stable (no "loss of time").

• Long-term use: documented for over 1 year, no habituation effects or diminishing of benefits.

• Contraindications: none absolute (also suitable for early risers – flexible choice allows for individual adaptation).

Limitations of the study

• Only two schools: Swiss context, transferability to other countries/school systems unclear.

• Observational study: no randomized control group (self-selection bias possible, but: 95% participation minimizes effect).

• Short follow-up period: 1 year – effects over several school years still unclear.

• Subjective endpoints: Fatigue & well-being via questionnaire (objective biomarkers such as cortisol are lacking).

• No data on extreme chronotypes: very early "larks" could theoretically be disadvantaged (but: no indication of this in the study).

⚠ Important note:

This information is for general informational purposes only and does not constitute medical advice. If you experience persistent sleep problems, extreme fatigue, or other health issues, please consult a doctor. The implementation of flexible school hours requires consultation with the school administration, teachers, and parents.

Sources

• Huber R, Milic J, et al. The Power of Flexible School Start Times: Longitudinal Evidence for Adolescents' Sleep, Health, and Academic Performance. Journal of Adolescent Health . 2026. DOI: 10.1016/j.jadohealth.2026.01.003

• University of Zurich. Start school later, sleep longer, learn better. Alpha Galileo . 2026. Link

• Earth.com . Flexible school start times improve teen health and learning. 2026. Link