The data sets contain all data and corresponding code books used for analyses in the research described in the SNIPPAA paper by van Woudenberg and Colleagues. The paper tests a social network intervention to promote physical activity in adolescents. In the study, 190 adolescents (46.32% boys; M age = 12.17, age range: 11–14 years) were randomly allocated to either the intervention or control condition. In the intervention condition, the most influential adolescents (based on peer nominations of classmates) in each classroom were trained to promote physical activity among their classmates. Participants received a research smartphone to complete questionnaires and an accelerometer to measure physical activity (steps per day) at baseline, and during the intervention one month later. The date files contain the physcial activity data per day, the sociometric nominations to determine the influence agents in the social network interventions classrooms, overview of the participants, a short evaluation of the influence agents, and the control variables at baseline and during the intervention (Background, Athletic competence, Attitude, Enjoyment, Intentions, Motivation, Self-reported physical activity, Sporting activities, subjective well-being, and a momentary assessment of happiness).