By analyzing data from a national panel survey of adolescents (ages 12-17) and their parents conducted around the 2008 general election, this study explores the varied roles communication plays in socializing youth into democratic citizenship. In particular, we propose and test a communication mediation model of youth socialization, in which interdependent communication processes located in the family, schools, media, and peer networks combine to cultivate communication competence, a set of basic communication skills and motives needed for active and informed participation in public life. Analysis of our panel data indicates that participation in deliberative classroom activities and democratic peer norms contribute to civic activism among youth. These peer and school influences, however, are found to be largely indirect, working through informational use of conventional and online news media, and expression and discussion of political ideas outside of classroom and family boundaries. In particular, our findings highlight strong online pathways to participation, centering on news consumption and political expression via digital media technologies, suggesting the key role of the Internet in this dynamic.