<p><strong>PURPOSE: </strong>The purpose of the study was to quantify changes in sleep during the middle-to-high school transition and determine if changes in sleep differ by sociodemographic characteristics.</p>

<p><strong>METHODS: </strong>Adolescents were enrolled in eighth grade and followed into ninth grade (N&nbsp;= 110; 2,470 nights observed). The outcomes were actigraphy-estimated sleep duration, sleep onset, sleep offset, and sleep sufficiency (≥8&nbsp;hours of sleep). The exposures were school grade (eighth or ninth), school night status (school or nonschool), sex (female or male), and race (white, black, or other).</p>

<p><strong>RESULTS: </strong>On school nights, sleep duration declined by 25.8&nbsp;minutes per night (p &lt; .001) from eighth to ninth grade. There was no change in sleep duration on nonschool nights. Timing of sleep onset was 22.2&nbsp;minutes later on school nights (p &lt; .001) and 17.4&nbsp;minutes later on nonschool nights (p&nbsp;&lt;&nbsp;.001) in ninth grade. Timing of sleep offset did not change on school mornings but was 22.2&nbsp;minutes later on nonschool mornings (p &lt; .001) in ninth grade. The proportion of school nights (and nonschool nights) with sleep duration ≥8&nbsp;hours was 9.4% (38.3%) in eighth grade and 5.7% (35.9%) in ninth grade. The odds of sleeping ≥8&nbsp;hours per night was 42% lower in ninth grade, compared toeighth grade (odds ratio&nbsp;= .58; 95% confidence interval: .37, .91). Males were 59% less likely to sleep ≥8&nbsp;hours per night. Black adolescents were 51% less likely to sleep ≥8&nbsp;hours per night.</p>

<p><strong>CONCLUSIONS: </strong>Insufficient sleep is highly prevalent, especially on school nights and among male and black adolescents, and this problem worsens with the transition to high school.</p>