This paper argues that the structure of activities provides the basis for a model of school organization and its effects on student outcomes. The observation is presented that it is within the context of daily activities that teachers and students make judgments about themselves and others, interact and form social ties, and experience social sanctions. It is stated that the structure of activities shapes the student's exposure to particular curriculum contents, the distribution and use of resources, the pedagogical decisions that teachers make, and the excercise of teacher authority. These, it is asserted, affect what children learn. The bases for this activity structures model in other work on social organization efforts are identified. Elements of the model are specified for different levels of schooling and the relationship between the structure of activities and other aspects of the schooling environment is described. Finally, associations are drawn between specific student outcomes and characteristic activity structures. (Author/APM)