This paper discusses early childhood education programs: their goals; effectiveness; optimal timing, targeting, and content; and costs and benefits. Early intervention has significant short- and medium-term benefits: most notably it reduces grade repetition and special education costs, and provides quality child care. The effects are greatest for more disadvantaged children. Some model programs have produced exciting improvements in educational attainment and earnings and have reduced welfare dependency and crime. The jury is still out on the long-term effects of Head Start, but Head Start would pay for itself if it produced a quarter of the long-term gains of model programs. (author abstract)