Despite the increased knowledge of the contextual determinants of implementation, the mechanisms leading to implementation success are not well understood. Explicating and testing program theories underlying implementation strategies designed through participatory processes involving intervention users with the expert knowledge of the practice context can lead to a better understanding of strategies that work in a real-world implementation. The purpose of this study was to identify facilitating and interfering contexts and mechanisms in implementing a pilot parenting intervention, Behavior Checker, as a part of routine service delivery in a rural primary care facility in the USA. This study was an organizational case study informed by the realist evaluation paradigm. Multiple methods of data collection were used, including key informant interviews with organizational representatives, a focus group and surveys with healthcare staff, and direct observation. The results indicated that the following mechanisms were central to facilitating and interfering with Behavior Checker implementation in the participating clinic: (1) staff knowledge and confidence; (2) complexity compression; (3) perceptions of sustainability; (4) workflow efficiency; (5) a systematic method of prompting intervention delivery and documentation; (6) capability for ongoing performance evaluation; (7) perception of fit; and (8) innovation-specific and general organizational resources. Understanding mechanisms can contribute to identifying strategies that support successful implementation and sustainable adoption of interventions that may benefit society.