RESUMO
Background: Sleeping and studying are the day-to-day activities of a teenager attending school. Aim: To determine the quality of sleep and its relationship to the academic performance among students attending morning and afternoon shifts in a public high school. Material and Methods: Students of the first and second year of high school answered an interview about socio-demographic background, academic performance, student activities and subjective sleep quality; they were evaluated using the Pittsburgh Sleep Quality Index (PSQI). Results: The interview was answered by 322 first year students aged 15 ± 5 years attending the morning shift and 364 second year students, aged 16 ± 0.5 years, attending the afternoon shift. The components: sleep latency, habitual sleep efficiency, sleep disturbance, drug use and daytime dysfunction were similar and classified as good in both school shifts. The components subjective sleep quality and duration of sleep had higher scores among students of the morning shift. The mean grades during the first semester of the students attending morning and afternoon shifts were 5.9 and 5.8, respectively (of a scale from 1 to 7). Among students of both shifts, the PSQI scale was associated inversely and significantly with academic performance. Conclusions: A bad sleep quality influences academic performance in these students.