Adolescents in high school suffer from circadian misalignment, undersleeping on weekdays and oversleeping on weekends. Since high schools usually impose early schedules, adolescents suffer from permanent social jetlag and thus are a suitable population to study the effects of social jetlag on both academic and cognitive performance. In this study, 796 adolescents aged 12 to 16 reported information about their sleep habits, morningness-eveningness, cognitive abilities and grade point average.Time in bed on both weekdays and weekends were not related to cognitive abilities, and only time in bed on weekdays was related to academic achievement. Social jetlag was negatively related to academic achievement, cognitive abilities (except for vocabulary and verbal fluency abilities) and general cognitive ability (g), whereas morningnesseveningness was slightly positively related to academic achievement and marginally negatively related to inductive reasoning. Results separated by sex/gender indicated that social jetlag may be more detrimental to girls' performance, as it was negatively related to a greater number of cognitive abilities and grade point average.

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Neither age nor sex was related to mood. However, the results indicated that regardless of chronotype mood increased throughout the school day from the lowest morning levels. Moreover, morning types showed better mood compared to other chronotypes, while evening types exhibited the lowest mood. Evening oriented students slept less than other chronotypes, but time in bed was not involved in the relationship between chronotype and mood. These results suggest that it is not shortened sleep duration responsible for decreased mood in evening oriented students.

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Interest to investigate daily fluctuations in cognitive tasks, so-called "school-rhythms", lies in exploring the most favourable time-of-day for learning considering the analysis of variations in performance taking into account individual differences. The aim of this study was to describe daily fluctuations in attention at three different times of the school day, two different days, considering chronotype and three different school start times (08:00, 08:15 and 08:30 h). Participants were 669 adolescents aged 12-16. Sleep length and inductive reasoning were considered as covariates. In general, attention increased throughout the school day, boys reached higher attention than girls and, moreover, evening type boys reached higher attention than evening type girls. No differences between chronotypes were observed. When students were familiar with the task, chronotype, sex and time-of-day interactions seem to be important factors to consider.