This study presents findings from a randomized effectiveness trial of the New Beginnings Program (NBP), which has demonstrated efficacy in 2 prior randomized efficacy trials. Family courts in 4 counties facilitated recruitment of divorcing and separating parents, and providers in community agencies delivered the program. Participants were 830 parents of children ages 3–18 who were randomized to receive either the 10-session NBP or an active 2-session comparison condition in which parents learned about the same parenting skills but did not complete home practice of these skills. Parents were ethnically diverse (59.4% non-Hispanic White, 31.4% Hispanic, 9.2% other race or ethnicity). Multiple rater assessments of parenting, interparental conflict, and child mental health problems were conducted at pretest, posttest, and 10-month follow-up. The results indicated positive moderated effects of the NBP as compared with the active control condition to strengthen parenting at posttest and to reduce child mental health problems at posttest and 10 months. Many of these moderated effects showed positive benefits for non-Hispanic White families but not for Hispanic families. The findings indicate support for the effectiveness of the NBP when delivered by community-based agencies but also indicate the need for further adaptations to make the program effective for Hispanic parents.