Sleep experts have determined a shift in sleep cycles (circadian rhythms) beginning in adolescence that makes it more difficult for most adolescents to fall asleep as early as younger children or older adults. Typical sleep cycles begin around 11 p.m. for teenagers and continue through 8 a.m.. This means that an early wake-up call (5 or 6 a.m. to allow many teens to catch buses or commute to early-start schools) not only allows 6 or 7 hours of sleep per school night at most but also requires students to wake up in the middle of deep sleep. According to most sleep experts, most adolescents need about 9 hours of sleep per night. Today nearly 2/3 get under 8, and 2/5 get under 6 hours of sleep per night.
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