ABSTRACT Despite the proliferation of fatherhood programs designed to promote paternal involvement and positive family outcomes, evaluations of these programs are scarce. The Supporting Father Involvement (SFI) study is a randomized clinical trial comprised of 289 low-income Spanish- and English-speaking families living in California. The evaluation design reflects a partnership stance that promotes empowerment of staff and social service agencies. This article examines lessons learned from the program’s first 3 years (2002?2004) from the perspectives of both evaluators and program staff. The lessons cover a broad range of areas, including communication procedures, training, staffing, recruitment/retention, clinical needs, intervention content and process, and maintaining cultural sensitivity.