This study uses data from the Early Childhood Longitudinal Study, Kindergarten Class of 1998-1999 (ECLS-K) to examine how children's skills and knowledge at kindergarten entry predict their achievement in later grades. It extends previous research by examining longer-term achievement outcomes, namely test scores at the end of fifth grade, and gives an indication of how the other nonacademic areas of school readiness (i.e., physical and socio-emotional development) may be related to test performance. This study addresses two research questions: (1) What is the relationship between children's school readiness skills at kindergarten entry and reading and mathematics achievement through the fifth grade; and (2) What kindergarten program factors predict the development of nonacademic school readiness skills? In particular, is attendance at a full-day program related to nonacademic school readiness? The study found that both academic and nonacademic school readiness skills at entry to kindergarten were significantly related to eventual reading and mathematics achievement in fifth grade. Attendance in a full-day kindergarten program was negatively associated with attitudes toward learning, self-control, and interpersonal skills, and was positively related toward internalizing (measured by a scale indicating presence of anxiety, loneliness, low self-esteem, and sadness) and externalizing behaviors. Instead, positive home background factors, such as higher income and higher parental involvement with the school, were associated with all five dimensions of nonacademic school readiness skills; higher income and more parental involvement were positively related to a child's attitudes toward learning, self-control, and interpersonal skills and negatively predictive of internalizing and externalizing actions. The analyses reinforce the findings of earlier studies that suggest that full-day kindergarten programs may not enhance achievement in the long term. It also suggests that investments in the development of nonacademic school readiness skills may not only raise overall achievement but may also narrow the achievement gap between minority and white students. The findings should help inform the debate about the merits of full-day kindergarten and should be of interest to educational researchers and education policymakers at the national, state, and local levels who are struggling with issues of school readiness and how to give all students an opportunity to learn to high standards. The following are appended: (1) Scale Items and Reliability Estimates; and (2) Descriptive Statistics of Scales for Waves 2-5. (Contains 12 figures and 14 tables.)