Time Mismatch: How School Schedules Drive Social Jet Lag and Sleep Deprivation Among Youth in Spain

Abstract Background School schedules play a central role in shaping how children and adolescents organize their daily life. As children grow, particularly during adolescence, their internal biological clocks naturally shifts to favour later sleep and wake times. These disruptions have serious implications for student's health, well-being and academic performance. In this study, we map patterns of social jetlag across age groups, gender and school schedule to better understand how school timing impacts students’ lives. Methods The sample includes 180 students (6 to 16 years of age; mean age is 12), enrolled. This is an ongoing longitudinal study, here we present the first wave of data collection that happened between 2023 and 2025 in primary schools or secondary (high) schools in the province of Valencia (Spain). We used the Munich Chronotype Questionnaire to assess the sleep-awake behavior on school and non-school days. The MCTQ asks about what time the individual goes to bed; what time he/she decides to sleep; how long it takes to fall asleep, to wake up, to get out of bed, and if an alarm clock was used. Additionally provides SJL (calculated by the difference between the midpoint of sleep in free and schooldays), chronotype (retrieved by the midpoint of sleep in free days sleep corrected) and the sleep dept. Results Our preliminary results show an average chronotype of 4.9, a social jetlag of 2.4, average sleep duration 8.4 (SD 1.4), average sleep loss is 2.6 hours (SD 2.4). We found no differences between sexes for social jetlag nor sleep loss nor chronotype. Conclusions School schedules are the main source of desynchronization for students. Social jet lag increases with age as students chronotypes delays and school entry times remain early or even advance in later ages where SJL is larger. For Spain problem may be even larger due to the misalignment between solar time and school time. Key messages • Delay school entry times to improve students’ health and performance. • Schools should synchronize to their local solar time.