Engaging and retaining participants are crucial to achieving adequate implementation of parenting interventions designed to prevent problem behaviors among children and adolescents. This study examined predictors of engagement and retention in a group-based family intervention across two versions of the program: a standard version requiring only parent attendance for six sessions and an adapted version with two additional sessions that required attendance by the son or daughter. Families included a parent and an eighth grader who attended one of five high-poverty schools in an urban Pacific Northwest school district. The adapted version of the intervention had a higher rate of engagement than the standard version, a difference that was statistically significant after adjusting for other variables assessed at enrollment in the study. Higher household income and parent education, younger student age, and poorer affective quality in the parent-child relationship predicted greater likelihood of initial attendance. In the adapted version of the intervention, parents of boys were more likely to engage with the program than those of girls. The variables considered did not strongly predict retention, although retention was higher among parents of boys. Retention did not significantly differ between conditions. Asking for child attendance at workshops may have increased engagement in the intervention, while findings for other predictors of attendance point to the need for added efforts to recruit families who have less socioeconomic resources, as well as families who perceive they have less need for services.