Background and Objectives: Intergenerational programs, those engaging youth and adults of nonadjacent generations in shared programming for mutual benefit, are attracting increasing attention from funders, policymakers, and practitioners for the range of goals they can support. The mechanisms by which these goals are achieved are rarely studied. To address this gap, we analyzed the associations between specific intergenerational implementation practices and younger and older participant outcomes. Research Design and Methods: Activity leaders at 5 sites serving adults and preschoolers received training to implement 14 evidence-based practices during intergenerational activities involving 84 adults (M = 75.25 years; range = 55–98) and 105 preschool participants (M = 3.26 years; range = 2–5) over 4 years. Measures of activity leaders’ implementation of these practices and participants’ behavioral responses to programming were gathered. We utilized multilevel modeling to test whether variations in implementation of practices were associated with variations in participants’ responses to programming on a session-by-session basis. (author abstract)