This study examines the process and effect of translating a pilot research project into a large-scale service program. In a pilot resource mothers program for pregnant teenagers, participants had fewer low birth weight infants than teenagers in the comparison group. In the corresponding large-scale service program, a similarly positive effect on low birth weight was not seen. In an effort to understand how these differences occurred, the evaluation methodologies and key characteristics that describe the background, infrastructure, components, and service providers of the two projects were compared. Important differences between the pilot project and the service program were seen in funding stability, diversity of staff, community versus health department ownership of the program, caseloads, and levels of training and supervision. It seems probable that these differences brought about changes in the intensity and character of the intervention from the pilot to the service program, leading to a reduction of the intervention's efficacy in reducing the number of low birth weight infants. The implications of these findings for researchers and program planners are discussed.