A significant number of children and adolescents are insufficiently physically active and have a sedentary lifestyle, which is associated with adverse health outcomes, necessitating effective interventions. Using a participatory approach, which engages youth in intervention development, may enhance intervention effectiveness, as such interventions are believed to be more tailored to the needs of the target group. This scoping review aimed to provide an overview of the results of process and effect evaluations of studies that developed school-based physical activity and/or sedentary behaviour interventions using a participatory approach among children and adolescents. Six databases (MEDLINE, Embase, Web of Science, CENTRAL (Cochrane Central Register of Controlled Trials), Scopus and SPORTDiscus) were searched. Studies were included when they evaluated the participatory process, intervention implementation or health-related intervention effects. A quality assessment was completed using two QualSyst checklists. Extracted data included characteristics of studies, interventions, and participatory processes; characteristics of participants from whom data were collected; outcomes measured and measurement methods used; and key findings. Twenty-five papers, covering 18 original studies, were included. Studies suggested that participatory processes were generally perceived positively, resulting in pupils feeling empowered, experiencing ownership and gaining certain skills. Participatory developed interventions also seemed to be generally well received, although the intervention dose delivered and intervention reach seemed to vary between studies. Finally, studies generally tended to report no effects on health. Although a participatory approach could be promising in empowering pupils and promoting intervention acceptance, apparent differences in intervention implementation and limited effectiveness highlight the need to enhance participatory processes and intervention effectiveness.