The ecological theory of teaching views the classroom as a unit within which social and psychological interactions determine the learning patterns that will take place. Three fourth-grade classrooms were observed to test and clarify this theory. A description is given of the characteristics of the pupils in each class, the teacher's instructional style and attitude, and the physical arrangement of the classroom. A comparison of the task structures of the three classes is presented, with emphasis on the grouping of students in large and small groups and the tasks assigned to those groups. An analysis is given of the relationship of the grouping and task assignments of the class to the formation of peer relations and friendships. (JD)