As a result of considering the limitations of the integrated models of educational effectiveness, a theory that takes into account the dynamic nature of education was proposed. The rationale and major assumptions of this theory are presented. Effectiveness factors operating at different levels and their measurement dimensions are outlined and the concept of grouping of factors is introduced. It is then argued that Educational Effectiveness Research should not only seek to identify cause-and-effect relationships between factors and student learning outcomes, but should also explain why and under which conditions each factor (or grouping of factors) has an effect on learning. For this reason, in this chapter, the importance of each factor included in the model that explains variation in student learning outcomes is explored by linking each factor with relevant theories concerning learning and school organisation.