Family dysfunction is unacceptably high nationally and internationally with high costs to society in adolescent problems. A number of evidence-based (EB) parenting and family interventions have been proven in research to improve children’s outcome. The question remains whether these EB family programs are as effective in practice. This article summarizes research outcomes from a quasi-experimental, 5-year statewide study of the 14-session Strengthening Families Program (SFP) with over 1,600 high-risk families. The study compared outcomes including effect sizes for the four different age versions of SFP (SFP 3–5, 6–11, 10–14, and 12–16 years). Quality assurance and program fidelity were enhanced by standardized training workshops, site visits by evaluators, and online supervision. Outcomes were measured using the SFP Parent Retrospective testing battery containing self-report standardized clinical measures of 18 parent, family, and child outcomes. The 2 repeated measures by 4 group ANOVA compared the four different age versions of SFP. All of the outcome variables for the four programs were statistically significant at less than the p d = .77 for SFP 6−11 years to effect size of d = .67 for SFP 3–5 and 10–14. The largest effect sizes were for improvements for the SFP 6–11 condition in Family Communication and Family Strengths and Resilience (d = .76 for both), Family Organization (d = .75), Parental Supervision (d = .73), Parenting Efficacy (d = .70), and Positive Parenting (d = .67). Parental alcohol and drug use was reduced most in the SFP 12–16 year version (d = .43). (PsycINFO Database Record (c) 2010 APA, all rights reserved)