A randomized trial evaluated the efficacy of 17 Early Head Start (EHS) programs. 3,001 low-incomefamilies with a pregnant women or an infant under 12 months wereassigned to a treatment or control group. Data were collected when children were 1, 2, 3, and 5 years old. Analyses examined (1) impacts at ages 2 and 3 (while services were being offered) and at age 5, and (2)contributions of early education experiences across childrens first 5years of life. Child outcomes included cognition, language, attention, behavior problems, and health; maternal outcomes included parenting, mental health, and employment. Mediated analyses identified whichimpacts at ages 2 and 3 contributed to child impacts at age 5. Growth curve analyses were also conducted. At ages 2 and 3, EHS benefited children and families in all domains. Significant family benefits were seen at age 5, and EHS children had better attention, approaches toward learning, and lower behavior problems than controls; however, they did not differ on early school achievement. Cognitive impacts were sustained 2 years afterthe program ended for African American children, as were language impacts for Hispanic children who spoke Spanish. Non-experimental analyses suggested that formal program participation in the 2 years following EHS enhanced childrens readiness for school while also increasing parent-reported aggression.At age 5, children and families who experienced EHS followed by formal programs fared best. However, benefits in language, behavior, and parenting were associated primarily with EHS; benefits inearly school achievement were associated primarily with preschool attendance.