The study described in this report was intended to provide researchers with comprehensive, longitudinal baseline data on average children and their families. The study focused on positive growth and development by identifying a national sample of children and families for researchers to study. The children were examined in five main areas: (1) relationships with parents, peers and teachers; (2) behavior; (3) socioemotional well being; (4) health, and access to health care; and (5) standardized test results. The study also examined factors affecting children's positive achievement and found that the following factors mattered most: (1) good health; (2) reading; (3) parental presence; and (4) positive parental/child relationship. The study also provided evidence to support the importance of: (1) educated parents; (2) verbally able parents; (3) parents with high expectations; and (4) parents who spend quality time with their children. The report is organized into five sections. Part one provides an introduction to the study, while part two, "Measuring Children's Well Being," describes five indicators of children's well-being. Part three, "How Well Are Children Doing?" analyzes the data on children's well-being by indicator. Part four, "What Matters Most for Children's Achievement and Adjustment?" explains the most important aspects of positive child development. The final section of the report summarizes the general study conclusions. (Author/SD)