Social capital theory states that civic engagement generates positive outcomes, such as social trust and political interest. Likewise, studies show that those involved in civic engagement generally report higher levels of social trust and political interest. It is still unclear, however, whether these differences are the result of socialization or selection. We used between-effects and fixed-effects regressions to examine the development of political orientations in a three-wave longitudinal sample of 1,050 adolescents. From our results, volunteering seemed to have no socialization effect whatsoever on political interest and potentially a weak enhancing effect on social trust. Associational membership did not predict social trust over time, but it seemed to socialize members into increased political interest over time. The results are discussed in light of the social capital debate about how civic engagemend in associational life and volunteering do - or do not - function as schools of democracy.