We examined variability and change in adolescents’ prosocial behaviors directed to peers and friends across four time scales: two-years, one-year, two-monthly, and daily. Data from three longitudinal datasets with a total of 569 adolescents (55.7% girl, M
age = 15.23, SD = 3.90) were included. The overall time-related stability of prosocial behavior across time scales was moderate to excellent. Variability did not differ between early (age 10–15) and late (age 16–21) adolescence, but late adolescence was associated with higher mean levels of prosociality. Finally, results indicated that prosocial behaviors measured over longer periods (i.e., two-years and one-year) were positively associated with cognitive processes (perspective taking), whereas prosocial behaviors measured over shorter periods (i.e., two-monthly) were positively associated with affective processes (empathy).