This paper examines shifts in social movement ties to political parties. It does so by focusing on three important contemporary Latin American movements: the student movements of Argentina, Chile, and Uruguay. Drawing on in-depth interviews with secondary and university activists in each country, the paper addresses two questions: First, why during the 1990s did student activists in all three countries increasingly organize outside and in opposition to parties? Second, why after 2000 did this autonomist trend partially fade in Argentina and Uruguay, but deepen in Chile? For both periods the paper seeks not only to identify key causal variables, but also to elucidate the causal mechanisms linking those variables to trends in movement ties to parties.