Sleep and waking behaviors change significantly during the adolescent years. The objective of this study was to describe the relation between adolescents' sleep/wake habits, characteristics of students (age, sex, school), and daytime functioning (mood, school performance, and behavior). A Sleep Habits Survey was administered in homeroom classes to 3,120 high school students at 4 public high schools from 3 Rhode Island school districts. Self-reported total sleep times (school and weekend nights) decreased by 40–50 min across ages 13–19, ps < .001. The sleep loss was due to increasingly later bedtimes, whereas rise times were more consistent across ages. Students who described themselves as struggling or failing school (C's, D's/F's) reported that on school nights they obtain about 25 min less sleep and go to bed an average of 40 min later than A and B students, ps < .001. In addition, students with worse grades reported greater weekend delays of sleep schedule than did those with better grades. Furthermore, this study examined a priori defined adequate sleep habit groups versus less than adequate sleep habit groups on their daytime functioning. Students in the short school-night total sleep group (<l6 hr 45 min) and/or large weekend bedtime delay group (>120 min) reported increased daytime sleepiness, depressive mood, and sleep/wake behavior problems, ps < .05, versus those sleeping longer than 8 hr 15 min with less than 60 min weekend delay. Altogether, most of the adolescents' surveyed do not get enough sleep, and their sleep loss interferes with daytime functioning.