To improve health outcomes of children, the US Maternal and Child Health Bureau has recommended more effective organization of preventive services within primary care practices and more coordination between practices and community-based agencies. However, applying these recommendations in communities is challenging because they require both more complex systems of care delivery within organizations and more complex interactions between them. To improve the way that preventive health care services are organized and delivered in 1 community, we designed, implemented, and assessed the impact of a health care system-level approach, which involved addressing multiple care delivery processes, at multiple levels in the community, the practice, and the family. Our objective was to improve the processes of preventive services delivery to all children in a defined geographic community, with particular attention to health outcomes for low-income mothers and infants. Observational intervention study in 1 North Carolina county (population 182 000) involving low- income pregnant mothers and their infants, primary care practices, and departments of health and mental health. An interrupted time-series design was used to assess rates of preventive services in office practices before and after the intervention, and a historical cohort design was used to compare maternal and child health outcomes for women enrolled in an intensive home visiting program with women who sought prenatal care during the 9 months before the program's initiation. Outcomes were assessed when the infants reached 12 months of age. Our primary objective was to achieve changes in the process of care delivery at the level of the clinical interaction between care providers and patients that would lead to improved health and developmental outcomes for families. We selected interventions that were directed toward major risk factors (eg, poverty, ineffective care systems for preventive care in office practices) and for which there was existing evidence of efficacy. The interventions involved community-, practice-, and family-level strategies to improve processes of care delivery to families and children. The objectives of the community-level intervention were: 1) to achieve policy level changes that would result in changes in resources available at the level of clinical care, 2) to engage multiple practice organizations in the intervention to achieve an effect on most, if not all, families in the community, and 3) to enhance communication between, among, and within public and private practice organizations to improve coordination and avoid duplication of services. The objective of the practice-level interventions was to overcome specific barriers in the process of care delivery so that preventive services could be effectively delivered. To assist the health department in implementing the family-level intervention, we provided assistance in hiring and training staff and ongoing consultation on staff supervision, including the use of structured protocols for care delivery, and regular feedback data about implementation of the program. Interventions with primary care practices focused on the design of the delivery system within the office and the use of teamwork and data in an "office systems" approach to improving clinical preventive care. All practices (N = 8) that enrolled at least 5 infants/month received help in assessing performance and developing systems (eg, preventive services flow sheets) for preventive services delivery. Family-level interventions addressed the process of care delivery to high-risk pregnant women (<100% poverty) and their infants. Mothers were recruited for the home visiting intervention when they first sought prenatal care at the community health center, the county's largest provider of prenatal care to underserved women. The home visiting intervention involved teams of nurses and educators and involved 2 to 4 visits per month through the infant's first year of life to provide parental education on fetal and infant health and development, enhance parents' informal support systems, and link parents with needed health and human services. We included training in injury prevention and discipline, and home visitors assisted mothers in obtaining care from one of the primary care offices. There were high levels of participation, changes in the organization of the delivery system, and improvements in preventive health outcomes. Agencies cooperated in joint contracting, staff training, and defining program eligibility. All 8 eligible practices agreed to participate and 7/8 implemented at least 1 new office system element. Of eligible women, 89% agreed to participate, and outcome data were available on 80% (180/225). After adjusting for differences in baseline characteristics, intervention group women were significantly more likely than comparison group women to use contraceptives (69% vs 47%), not smoke tobacco (27% vs 54%) and have a safe and stimulating home environment for their children. Intervention group children were more likely to have had an appropriate number of well-child care visits (57% vs 37%) and less likely to be injured (2% vs 7%). Intervention mothers also received Aid to Families with Dependent Children for fewer months after the birth of their child (7.7 months vs 11.3 months). We observed a number of positive effects at all 3 levels of intervention. Policy-level changes at the state and community led to lasting changes in the organization and financing of care, which enabled changes in clinical services to take place. These changes have now been expanded beyond this community to other communities in the state. We were also able to engage multiple practice organizations, reduce duplication, and improve the coordination of care. Changes in the process of preventive services delivery were noted in participating practices. Finally, the outcomes of the family-level intervention were comparable in direction and magnitude to the outcomes of previous randomized trials of the intervention. All the changes were achieved over a relatively brief 3-year study period, and many have been sustained since the project was completed. Tiered, interrelated interventions directed at an entire population of mothers and children hold promise to improve the effectiveness and outcomes of health care for families and children.