We investigate class differences in youth activity participation with interview, survey, and archival data from a diverse sample of parents (n = 51) in two schools. Findings point toward structural rather than cultural explanations. Working- and middle-class parents overlap in parenting logics about participation, though differ in one respect: middle-class parents are concerned with "customizing" children's involvement in activities, while working-class parents are concerned with "ensuring" safety and social mobility for children through participation. Like financial constraints among the working class, social institutions are implicated in class differences. Schools act as an equalizing institution by offering low-cost activities; yet, contribute to class differences by offering different activities to working- and middle-class youth. Opportunities for working-class youth to participate in non-school activities are few due to the scarcity of community organizations in their neighborhood, while middle-class families are heavily involved in out-of-school activities. We explore the implications of our findings for educational stratification. (Contains 5 figures, 3 tables and 15 notes.)