After genetics, the most important factor in one’s chronotype is age. As parents know and lament, young children are generally larks. They wake up early, buzz around throughout the day, but don’t last very long beyond the early evening. Around puberty, those larks begin morphing into owls. They wake up later—at least on free days—gain energy during the late afternoon and evening, and fall asleep well after their parents. By some estimates, teenagers’ midpoint of sleep is 6 a.m. or even 7 a.m., not exactly in synch with most high school start times. They reach their peak owliness around age
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