According to Kelly & Lee (2015), “Adolescence starts with the onset of puberty and ends in the early 20s” (p. 1). The delay in sleep-wake times can continue on into the early 20s (Roenneberg et al., 2007).However, school start times do not accommodate the biological changes of adolescents (Ming et al.,2011). Many adolescents end up sleeping later but waking earlier to accommodate the school start times, reducing the amount of sleep obtained causing sleep deprivation (Ming et al.,2011).
Due to this, adolescents can lose approximately 2.7 hours of sleep on school days (Foster et al., 2013). Studies show that the sleep lost on weekdays accumulates into sleep debt and can only be paid off with a few days of good sleep (Crowley, Acebo, & Carskadon, 2007). A decline in academic performance and cognitive functioning has been linked to sleep debt (Preckel et al., 2013; Telzer, Fuligni, Lieberman, & Galván, 2013). In addition, waking later than usual on weekends caused melatonin to be released even later the following week, causing the circadian disruption to worsen (Taylor, Wright, & Lack, 2008; Crowley & Carskadon, 2010).
Studies have shown that later school start times do increase sleep duration and decrease daytime sleepiness. Martin et al. (2016) found that students in afternoon school did not need to compensate for sleep debt as they had adequate sleep on weekdays. Students that had morning classes had less sleep and felt sleepier during the day, compared to the students who attended afternoon class (Martin, Gaudreault, Perron, & Laberge, 2016; Ming et al., 2011).
The students that had morning classes, slept earlier on weekdays than on weekends, displaying a difference in sleep wake patterns between weekdays and weekends, that is a result of the discrepancy between the sleep wake pattern and circadian rhythm (Martin, Gaudreault, Perron, & Laberge, 2016). One study showed that the average adolescent moved forward their bedtime and rise time to adjust to school demands (Ming et al.,2011).