The aim of this project was to compare circadian rhythmicity of a group of 37 adolescents (14 girls), aged 11 to 16 (mean age = 13.1 +/- 1.7 years), with and without electricity at home. Twenty students attended morning school (07:30-11:30), and 17 attended evening school classes (19:00-22:30). Eleven adolescents had no electric lighting at home (5 attended morning classes and 6 attended evening classes). They completed a sleep log and wore a wrist actigraph for 5 consecutive days. Saliva samples were collected to assess DLMO. Data were compared by ANOVA and showed later timing and a more extended sleep period for those who attended late classes. Those adolescents without electricity at home had significantly earlier sleep onset on school days. As to DLMO, a trend to a delay was observed in the groups who had electric lighting.