Age and gender differences in morningness-eveningness during adolescence.

Morningness-eveningness was assessed in a large sample of adolescents and young adults. Morningness decreased from 12 to 15 years, and then remained on a stable level until about 20 years, when a turn back to morningness occurred. Boys and men were on average more evening-oriented than were girls and women. In detail, significant differences existed at the ages of 16, 18, and 19 years. A quadratic function explained more variance than a linear regression. Composite Scale of Morningness scores are related to puberty scores in boys and girls, and when combining data (i.e., higher pubertal development was related to eveningness).