An ecological approach was used to gather data about properties of purpose, human behavior, and setting as they unfolded in classrooms. Participating were 11 elementary school districts in the Chicago Standard Metropolitan Statistical Area; districts were stratified by median family income (low, middle, high) and per pupil expenditure (low, high). Classroom transactions were analyzed by examining the activity structure and its activity segments. Activity structure within the classroom was defined as being the main tasks or types of activities in which the children and teacher participate. An activity segment was defined as a unique time block in a lesson occurring in a fixed physical setting. In the investigation, main variables of interest were segment properties and measures of student involvement in segments. Observations were made of eight students each in math and social studies classrooms within each district. Findings indicated that children's involvement in math and social studies classrooms was virtually identical. Student involvement was related to type of pacing and cognitive level of segments. A clear pattern of increasing involvement as a function of cognitive complexity was found to be present in both sets of subjects, and children's average involvement was highest when they were working cooperatively. Further, the function of a segment in the activity flow had a clear impact on student attention. (Sample instruments, coding definitions, classroom descriptions, and tables of data are appended.) (RH)