As Time Goes By: Effects of Basal Chronotype and School Timing on Chronotype Development During Adolescence

The misalignment between late chronotypes and early school start times affect health, performance and psychological well-being of adolescents. Here we test whether, and how, the basal chronotype (i.e. chronotype at the beginning of secondary school) and the school timing affect the magnitude and the direction of the developmental change in chronotype during adolescence. We evaluated a sample of Argentinian students (n=259) who were randomly assigned to attend school in the morning (07:45am-12:05pm), afternoon (12:40pm-05:00pm) or evening (05:20pm-09:40pm) school timings. Importantly, chronotype and sleep habits were assessed longitudinally in the same group of students along secondary school (at 13-14 y.o. and 17-18 y.o.). Our results show that: (1) although chronotypes partially align with class time, this effect is insufficient to fully account for the differences observed in sleep-related variables between school timings; (2) both school timing and basal chronotype independently affect the direction and the magnitude of chronotype change, with greater delays associated with earlier basal chronotypes and later school timings. The practical implications of these results are challenging and should be considered in the design of future educational timing policies to improve adolescents’ well-being.

O030 Changes in sleep-wake patterns, circadian timing, and mood in Australian teens during the COVID-19 pandemic

During the COVID-19 pandemic, schools rapidly transitioned from in-person to remote learning. We examined sleep- and mood-related changes in early adolescents, before and after this transition to assess the impact of in-person vs. remote learning. Sleep-wake timing was measured using wrist-actigraphy and sleep diaries over 1–2 weeks in Year 7 students (age M±SD =12.79±0.42 years) during in-person learning (n=28) and remote learning (n=58; n=27 were studied in both conditions). Circadian timing was measured under a single condition in each individual using salivary melatonin (Dim Light Melatonin Onset; DLMO). Online surveys assessed mood (PROMIS Pediatric Anxiety and Depressive Symptoms) and sleepiness (Epworth Sleepiness Scale – Child and Adolescent) in each condition. During remote vs. in-person learning: (i) on school days, students went to sleep 26 min later and woke 49 min later, resulting in 22 min longer sleep duration (all p<0.0001); (ii) DLMO time did not differ significantly between conditions, although participants woke at a later relative circadian phase (43 minutes, p=0.03) during remote learning; (iii) participants reported significantly lower sleepiness (p=0.048) and lower anxiety symptoms (p=0.006). Depressive symptoms did not differ between conditions. Changes in mood symptoms were not mediated by changes in sleep timing. Although remote learning had the same school start times as in-person learning, removing morning commutes likely enabled adolescents to sleep longer, wake later, and to wake at a later circadian phase. These results indicate that remote learning, or later school start times, may extend sleep duration and improve some subjective symptoms in adolescents.

COVID-19 instructional approaches (in-person, online, hybrid), school start times, and sleep in over 5,000 U.S. adolescents

Study Objectives To examine associations among instructional approaches, school start times, and sleep during the COVID-19 pandemic in a large, nationwide sample of U.S. adolescents. Methods Cross-sectional, anonymous self-report survey study of a community-dwelling sample of adolescents (grades 6–12), recruited through social media outlets in October/November 2020. Participants reported on instructional approach (in-person, online/synchronous, online/asynchronous) for each weekday (past week), school start times (in-person or online/synchronous days), and bedtimes (BT) and wake times (WT) for each identified school type and weekends/no school days. Sleep opportunity was calculated as BT-to-WT interval. Night-to-night sleep variability was calculated with mean square successive differences. Results Respondents included 5,245 racially and geographically diverse students (~50% female). BT and WT were earliest for in-person instruction; followed by online/synchronous days. Sleep opportunity was longer on individual nights students did not have scheduled instruction (>1.5 h longer for online/asynchronous than in-person). More students obtained sufficient sleep with later school start times. However, even with the same start times, more students with online/synchronous instruction obtained sufficient sleep than in-person instruction. Significantly greater night-to-night variability in sleep-wake patterns was observed for students with in-person hybrid schedules versus students with online/synchronous + asynchronous schedules. Conclusions These findings provide important insights regarding the association between instructional approach and school start times on the timing, amount, and variability of sleep in U.S. adolescents. Given the public health consequences of short and variable sleep in adolescents, results may be useful for education and health policy decision-making for post-pandemic secondary schools.

Are flexible school start times associated with higher academic grades? A 4-year longitudinal study.

The mismatch between teenagers' late sleep phase and early school start time results in acute and chronic sleep reductions. This is not only harmful for students' learning in the short-term but may impact on students' career prospects and widen social inequalities. Delaying school start times has been shown to improve sleep but whether this translates to better achievement is unresolved. The current evidence is limited due to a plethora of outcome measures and the many factors influencing sleep and grade/score trajectories. Here, we studied whether 0.5-1.5 years of exposure to a flexible school start system, with the daily choice of an 8AM or 8:50AM-start (intervention), allowed secondary school students (n=63-157, 14-19 years) to improve their quarterly school grades in a 4-year longitudinal pre-post design. We investigated whether sleep, changes in sleep or frequency of later starts predicted grade improvements in the flexible system. Our mixed model regressions with 5,111-16,724 official grades as outcomes did not indicate meaningful grade improvements in the flexible system per se or with previously observed sleep variables (nor their changes) - the covariates academic quarter, discipline and grade level had a greater, more systematic effect in our sample. Importantly, this finding does not preclude improvements in learning and cognition in our sample. However, at the 'dose' received here, intermittent sleep benefits did not obviously translate into detectable grade changes, which is in line with several other studies and highlights that grades are suboptimal to evaluate timetabling interventions despite their importance for future success.