This study of 119 preschool programs in 5 states was designed to describe the classroom experiences of economically or educationally disadvantaged 4-year-old children and to examine linkages between characteristics of early childhood programs and the activities of the children and teachers in the classroom. Chapters 1 and 2 describe the context for the study and the study design. Chapter 3 reports the characteristics of the programs, classrooms, and staff observed, while chapter 4 chronicles the classroom day with regard to activities, groupings, and supervision. Chapters 5 and 6 examine interactions in the classroom and the measurement and prediction of the quality of the classroom experience, while chapter 7 presents the study's conclusions. Among the findings are that: (1) preschoolers spent over half their time in activities believed to foster cognitive growth; (2) in a substantial number of classrooms, activities that would be expected to be included in the daily curriculum, such as story-time or science and natural world activities, did not occur; and (3) lower child to staff ratios, higher teacher education levels, and higher levels of parent involvement were associated with all global measures of classroom quality. Implications of these results are also discussed. Three appendixes provide supporting tabular data, a profile of the "classroom snapshot" observational tool, and descriptions of four global quality measures. Includes 73 references. (MDM)