"A Study of Schooling" is an in-depth descriptive study of 38 purposively sampled schools in the United States. Many aspects of the educational process were examined, from student attitudes to principal leadership styles. Essential to this comprehensive view of education is a view of within classroom processes, including teacher student interaction patterns, leadership modes, availability of materials, and grouping tendencies. This report provides a methodological overview of the observation system that was used to collect this classroom data, including a description of the instrument, the selection and training of observers, data reduction and definition of variables, and summary reports generated at the class, school, and subject levels of analysis. Appended are: (1) the five sections of the classroom observation instrument; (2) observer's manual; (3) variable specifications; (4) summary report on three sections of the instrument: physical environment inventory, daily summary, and classroom snapshot; and (5) summary report on another section: five-minute interactions. (JD)