With the launch of the U.S. Department of Education's Early Childhood Longitudinal Study, Kindergarten Class of 1998-99, measures of knowledge, skills, health, and behavior of a large and nationally representative sample of American Kindergartners are available. Drawing on data from the study, this report provides a portrait of kindergarten children in the areas of reading, mathematics, and general knowledge, as well as noncognitive aspects of school readiness. The report details: (1) what a typical child knows at school entry; (2) what the typical child's health and behavior are like at school entry; (3) what factors help account for variations in knowledge, health, and behavior at school entry; (4) what sex-related differences in school readiness exist for kindergartners; (5) what family background characteristics affect children's skills and knowledge; and (6) how risk factors affect noncognitive aspects of school readiness. Among the findings are the following: (1) most children know their letters and can count more than 10 objects; (2) most are in very good to excellent health, though some experience developmental difficulties; (3) most are reasonably well behaved and exhibit a positive approach to classroom tasks; (4) some have advanced skills while others lag behind; (5) age is a factor in variations in knowledge, health, and behavior; (6) girls and boys have similar skills, although girls are slightly ahead in reading; (7) more boys experience developmental difficulties; (8) girls are more prosocial and less prone to problem behavior; (9) nearly half of all entering kindergartners come from families with one or more risk factors in the areas of parental education, socioeconomic status, and family structure; (10) minority children are more likely to be at risk; (11) risk factors are linked to poorer child health; (12) at-risk children are less likely to be socially adept and more likely to be aggressive; and (13) fewer at-risk children have a positive attitude toward learning activities. (Contains 40 references.) (HTH)