The aim of this study was to examine the convergent validity of self-reported diary times for commuting to and from school with device-measured positional data (Global Positioning System; GPS) in Spanish adolescents. Cross-sectional data were obtained from four Spanish public secondary schools in 2021, comprising 47 adolescents and 141 home-school and school-home trips. Participants self-reported the time they left and arrived at home and school through a commuting diary. They wore a GPS device recording the objective time during three trips (i.e., one home-school trip and two school-home trips). Agreement between commuting diary and GPS data regarding home-school trips and school-home trips was evaluated using Bland-Altman plots. Total commuting time differed by 1 min (95% limits of agreement were 16.1 min and -18.1 min) between subjective and objective measures (adolescents reported 0.8 more minutes in home-school trips and 1 more minute in school-home trips compared to objective data). Passive commuters reported 0.7 more minutes and active commuters reported 1.2 more minutes in the total commuting time compared to objective data. Self-reported commuting diaries may be a useful tool to obtain commuting times of adolescents in epidemiological research or when tools to measure objective times are not feasible.