<p>Understanding the interplay between political participation and political efficacy is crucial for fostering democratic engagement. This two-wave panel study investigated the potentially reciprocal relationship between non-institutionalized political participation and internal and external political efficacy among adolescents. The study drew on a German sample of 444 students from Grade 7 and Grade 8 (wave 1: <i>M</i>_age = 12.94, <i>SD</i>_age = 0.61; 46.9% female). It examined whether and how internal and external political efficacy are related to participation and whether participation, in turn, is related to political efficacy over time. Results revealed low stability for external political efficacy and non-institutionalized participation and moderate stability for internal political efficacy between Grade 7 and Grade 8. When students’ demographics were controlled for, internal political efficacy in Grade 7 was positively related to non-institutionalized participation in Grade 8, but no significant effects of participation on efficacy were observed. This study provides initial insights into the relationship between open democratic practices, like petitioning, protesting, and boycotting, and adolescents’ perceptions of political efficacy. Results suggested that the transformative potential of participatory activities may depend on specific conditions. The findings highlight the need for further research to explore these dynamics longitudinally and across different forms of participation.</p>