Citizen science research has been rapidly expanding in the past years and has become a popular approach in youth education. We investigated key drivers of youth participation in a citizen social science school project and the effects of participation on scientific and topic-related (i.e., political) interest and efficacy. Findings suggest that females, more politically and scientifically interested and more scientifically efficacious adolescents were more motivated to learn from the project. Science efficacy was also positively related to external reward motivation (i.e., winning an award). Both learning and external reward motivation increased the likelihood of participation. Pre- and post-measurement further indicated that participation in the project slightly increased science interest, but not science efficacy. However, it did increase both political interest and efficacy. Furthermore, our data revealed a decrease in science efficacy and interest in those who did not participate in the project, indicating an increasing gap in adolescents' scientific involvement.