This study was designed to test hypotheses about family risk factors and their links to dosage and efficacy of a family-centered preventive intervention. Participants were 172 families with an 11 year-old child randomly assigned to the intervention condition in the Strong African American Families Program (SAAF). Two family risk factors, ratio of adults to children in the household and youth unconventionality, were negatively related to dosage, defined as number of intervention sessions attended. Dosage, in turn, was associated with changes in targeted parenting behavior across the 7 months between pretest and posttest. The effect of family risk factors on the link between program dosage and changes in parenting behavior was stronger for families experiencing more risks. The results highlight the need for engagement strategies for recruiting and retaining high-risk families in preventive interventions.