Using data collected up to age 26 in the Chicago Longitudinal Study, this cost-benefit analysis of the Child-Parent Centers (CPC) is the first for a sustained publicly funded early intervention. The program provides services for low-income families beginning at age 3 in 20 school sites. Kindergarten and school-age services are provided up to age 9 (third grade). Findings from a complete cohort of over 1,400 program and comparison group participants indicated that the CPCs had economic benefits in 2007 dollars that exceeded costs. The preschool program provided a total return to society of $10.83 per dollar invested (18% annual return). The primary sources of benefits were increased earnings and tax revenues and averted criminal justice system costs. The school-age program had a societal return of $3.97 per dollar invested (10% annual return). The extended intervention program (4-6 years) had a societal return of $8.24 (18% annual return). Estimates were robust across a wide range of analyses including Monte Carlo simulations. Males, 1-year preschool participants, and children from higher risk families derived greater benefits. Findings provide strong evidence that sustained programs can contribute to well-being for individuals and society. (Contains 5 tables and 2 figures.)