ObjectivesTo examine the sleep pattern and observe differences in sleep routines, phase preferences, mood, attendance, and academic performance among different adolescent age students. Secondly, to observe the age at which sleep phase transition and changes in sleep requirement become evident.MethodsA cross-sectional study was conducted among 501 students (aged 11-15 y) of a school in Delhi, India. Students were evaluated for their sleep patterns, sleep duration, habits of napping, quality of sleep, sleepiness, depression, phase preferences by self-reported school sleep habits survey questionnaire along with school performance and attendance.ResultsSignificant differences were found in sleep pattern of students aged 11-12 y and 13-15 y. Bedtime shifted to a later time with increasing age but early morning schools kept the wake time same, leading to a decline in total sleep duration of older adolescents. Older adolescents had higher depression but poor attendance and academic performance. Prevalence of sleep deprivation increased with age, from 83.7% to 87.1% in 11-12 y to 90.5% to 92.5% in 13-15 y.ConclusionsThe study clearly identifies 12-13 y as age of transition of sleep pattern among adolescents. Though significant differences were found in the academic performance, mood and attendance among preteens and teens but no direct association was seen between academic performances and sleep pattern. A complex multifactorial association between sleep patterns, attendance, mood and academic performance which may change over days, months, or years should be explored further in a longitudinal follow up study.