Because they often set out with a guarantee of only short-term funding, many community partnerships will face a threat to their sustainability almost as soon as the first money runs out. Research into the factors that enable some coalitions and partnerships to meet the challenge when others fail is limited. This study begins to fill this gap in our understanding by examining influences on the process of sustainability planning in the context of a collaborative partnership focused on youth development. We report on a longitudinal examination of the quality of planning and attitudes underpinning the sustainability of PROSPER community prevention teams whose members implement evidence-based programs designed to support positive youth development and reduce early substance use and other problem behaviors. The current research concentrates on a particular dimension of partnership effectiveness to establish whether perceptions about team functioning in play at 6 and 18 months predict the quality of sustainability planning at 36 and 48 months. How well teams functioned in the early stages was found to be strongly related to the quality of their later preparations for sustainability. Recruitment and integration of new team members, and the encouragement they subsequently received were also found to be key factors. The results strengthen the argument for providing technical assistance to meet the needs of those who promote prevention partnerships, and they provide longitudinal empirical data to support the hypotheses of other researchers who have similarly found a correlation between effective sustainability and early planning and support.