We describe the contributions of cognitive-scholastic advantage, family support behavior, and school quality and support as processes through which early childhood interventions promote the well-being of vulnerable children and families. Evidence in support of these processes is from longitudinal cohort studies of the Child-Parent Centers and other preventive interventions beginning in the first few years of life. Relatively large effects of program participation have been documented for school readiness skills, parent involvement, K-12 achievement, reduced need for remedial education, educational attainment, and crime prevention. The three processes account for up to half of the program impact on well-being. They also help to explain the positive economic returns of many effective programs. The generalizability of these processes is supported by a sizable knowledge base, including a scale-up of the Child-Parent Centers in two states.