The study of educational effectiveness has become increasingly complex. Alongside methodological advancements in the investigation and measurement of educational effectiveness, meta-analyses conducted by leading researchers have shown that the field has been suffering from a significant lack of theory or from a weak theoretical basis. The present paper seeks to address this gap by connecting the four models of organisational effectiveness incorporated in Quinn and Rohrbaugh's framework of competing values to the four dualities of educational design that appear in Wenger's theory of communities of practice. By doing so, the paper contributes theoretical insights towards the development of a dilemmatic approach to the study of educational effectiveness. Based on the theoretical insights offered here, the paper argues that effective educational organisations are those that are able to address successfully and on an ongoing basis paradoxical tensions and incorporate interrelated and yet contradictory elements of the educational process and school organisation.