Purpose: There is scant child welfare research on parenting interventions for parents with intellectual and developmental disabilities (I/DD). This mixed-methods research examined client participation in an in-home parenting intervention, including client characteristics, which clients benefit most from participation, and key aspects of program participation. Method: The sample included participant program records, client satisfaction surveys, stakeholder interviews, and a staff focus group. The quantitative data were analyzed using growth curves and binary logistic regression. The qualitative data were analyzed using thematic analysis. Results: Time spent in Project Improving Parenting Achievements Together was predictive of improvement in parenting skills and the home environment and reduction in the odds of out-of-home placement for children of parents with I/DD. The intensity of services, tailored education, community engagement, and client–worker relationship were the key aspects of program participation. Discussion: With proper supports, parents with I/DD can learn parenting skills, improve the home environment, and keep their family intact.