The present study found that school starting time earlier than 07:00 and more time spent on homework were significant predictors for insufficient sleep duration, a finding similar to our previous study conducted among school-aged children [30]. Our study also showed, for the first time, that cram school learning was a significant predictor among Chinese adolescents. School schedules reflect certain cultural attributes and traditions of a nation. It is well known that Chinese students, especially high school students, are burdened with tremendous academic pressure even to the extent of sacrificing sleep time. Out with the regular school academic schedule, many students have an extra learning plan. The present study demonstrated that as high a proportion as 63.9% of Chinese adolescents attended extracurricular learning classes.