The toll of an early bell? School start time and adolescent sleep quality in Flanders, Belgium

A 10-minute delay in school start time in Flemish secondary schools is linked to non-significant changes in adolescent sleep quality (0.01/1–5) and school-day sleep duration (3.5 minutes).

• Why it matters: Early start times could clash with puberty-related sleep timing, but evidence on whether small schedule shifts affect adolescent sleep duration and quality is needed.
• What they did: Using 2022 Flemish HBSC data (12,329 adolescents in grades 1–6 across 94 secondary schools), the study related school start times to self-reported sleep duration and sleep quality with linear regression and debiased machine learning.
• The result: Confidence intervals excluded clinically meaningful effects of later start times within the observed narrow range, implying larger delays may be required to see benefits.

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