Sleep undergoes important changes during adolescence and many teenagers experience problems sleeping. These in turn affect adolescents´ academic, physical and psychosocial functioning. Moreover, there are some indications that sleep problems in this age group may be increasing, possibly as a consequence of societal changes, e.g., internet availability. Research on adolescents´ sleep is growing, but more epidemiological studies are needed to clarify the prevalence of poor sleep, long and short-term outcomes associated with it, and potential risk and protective factors to target in preventive interventions. The aim of this dissertation was to contribute to each of these goals; Study I investigated the longitudinal association between sleep problems, defined as symptoms of insomnia, and school absenteeism; Study II explored the prevalence of poor sleep, defined as sleep deficit, in an adolescent population and psychosocial and contextual factors associated with it, including emotional and behavioral problems, stress, sleep hygiene and technology use; finally, Study III evaluated the short-term effects of a novel universal school-based intervention to improve adolescents´ sleep health. The findings show that poor sleep was strongly related to adolescents´ functioning, including emotional and behavioral problems and school attendance, and that sleep deficit was prevalent in adolescents. This supports the need for prevention. Moreover, sleep deficit was associated with stress, technology use and arousal at bedtime, which may represent important barriers to sleep. A preventive intervention targeting these barriers to promote adolescents´ sleep health was successful with the individuals most at risk. However, it remains to be seen whether these changes will be maintained after the intervention and whether incidence of sleep problems will be lower relative to a control group. Implications for theory and practice are discussed.

There is a noticeable difference in the debate regarding adolescents’ sleep patterns between the biological clock and society’s clock when we talk about adolescents. Sleep scientists or somnologists, are alarming as more evidence reach the surface that young people are not getting the recommended sleep that is required to perform academically well. Not only are there direct connections between sleep deficit and academic performance, but sleep deficit also takes a critical toll upon their physical and mental health. The problem is that adolescents’ circadian cycle is postponed with a few hours compared to children and adults. This results in a major sleep deficit when adolescents must adjust to societal rhythms and habits – a clock they are not programmed biologically to follow. Adolescents must attend to school in the early morning, when in reality their needs point to that school times in fact should start around 10:00. Society’s view has traditionally been that teenagers are lazy but in fact evidence does prove that it may not be the case. The following essay will therefore serve as an informative update to what has been stated by somnologists and raise awareness regarding adolescents and what happens when they are exposed to a chronic sleep deficit put on them by society.