We know little about why school administrators choose to adopt preventive mental health interventions within the context of school-based prevention trials. This study used a qualitative multiple-case study design to identify factors that influenced the adoption of a trauma-informed universal intervention by urban public school administrators during an efficacy trial. Semi- structured interviews were conducted with 15 school administrators who adopted a trauma-informed mindfulness intervention called RAP (Relax, be Aware, and do a Personal Rating) Club as part of their participation in a school-based trial with eighth graders. Findings indicated that administrators adopted RAP Club to provide support for students affected by trauma and prevent students from engaging in unhealthy coping behaviors. Examples of contextual factors that contributed to adoption included a lack of trauma-informed mental health programs within schools, inadequate district funding for preventive school mental health services, and the perceived benefits of engaging in a university-community partnership. The study's findings suggest strategies to increase school program adoption in the context of research and, more broadly, for implementation science. [This is the online first version of an article published in "Prevention Science."]