A growing body of literature has linked chronotype and sleep to school performance. Chronotype is under the control of the circadian clock and refers to sleep timing and diurnal preferences. Chronotype changes with age and is latest during adolescence, giving rise to a mismatch between the (late) circadian clock and the (early) school clock. In general, evening (late) chronotypes obtain lower grades. School performance is influenced by many other factors, such as motivation, intelligence, and conscientiousness. Some of these factors also relate to chronotype. The present paper reviews the literature on the relationship between chronotype and school performance, with the aim of suggesting hypotheses about the mechanisms behind this complex phenomenon and exploring solutions for an optimized school system. Based on the literature reviewed, we hypothesize that chronotype has both a direct and an indirect effect on school performance. The indirect effect is mediated by factors such as conscientiousness, learning/achieving motivation, mood, and alertness. In addition, time of day of testing plays an important role since the chronotype effect on grades is strongest in the morning and disappears in the afternoon. Strategies to decrease the mismatch between the adolescent circadian clock and the school clock could involve light interventions to advance the students' sleep timing, delays in school starting times, and rearrangements of test schedules (tests later in the day).
