The Supporting Effective Teaching project commenced in the early 1990s with studies of how classroom teachers work with students with special educational needs included in their elementary classrooms. Over the ensuing 20 years, the project team prepared and tested a model of the factors that influence student outcomes in inclusive classrooms, with emphasis on the beliefs and practices of regular elementary classroom teachers and on their sense of responsibility for meeting the diverse learning needs of their students. This article provides an overview of the SET project to show how the model evolved and to bring together the findings that were published previously. It takes a different tack from previous papers in that it begins at the most surprising outcome, the importance of teaching practices. Arguably the most significant empirical finding from the project is that teachers who believe it is their responsibility to include students with special education needs are more effective practitioners for all their students. The article then traces the factors that contribute to this finding: quality of instruction, teacher beliefs about ability and disability, teacher beliefs about learning and instruction, and school context. The purpose is to present a comprehensive review of the project findings in the context of recently published research on inclusion. [For "The Supporting Effective Teaching Project: 2. The Measures," see EJ1200793.]