Out-of-school time (OST) programs represent a vital opportunity and resource for learning and development for children and youth. Given the potential of city-level OST initiatives to support participation, and against the national backdrop of inequitable access to quality OST programs for older youth from disadvantaged communities, The Wallace Foundation commissioned this research study. To understand how to promote sustained participation in OST programs, this study examined the program characteristics--both program practices and structural features--associated with high participation and retention that were employed by OST programs, primarily serving disadvantaged youth, in six cities that have worked toward building OST initiatives. In particular, this report addresses how OST programs keep middle and high school youth engaged over time (i.e., the duration of participation) and how the supports that city initiatives provide can help foster youth participation, with the assumption that programs can have a potentially greater impact if they are able to work with these youth over an extended period of time. Appendices include: (1) Cities and Initiatives; (2) Youth Participation Community of Practice; (3) Respondent List; (4) Sample Selection and Description; (5) Analysis Description; (6) Twenty-Eight Programs/Organizations Interviewed; and (7) Practices and Features of High-Retention Programs. (Contains 31 tables, 23 footnotes, and 72 notes.) ["Engaging Older Youth: Program and City-Level Strategies to Support Sustained Participation in Out-of-School Time" was written with Diana Lee.]