Résumé : In this doctoral thesis, composed of 7 scientific articles, I have developed a framework for analyzing how assumptions about knowledge and knowledge learning ("epistemological assumptions") inform distinct educational theories and approaches. This framework involves an analysis at several levels: (a) the epistemological assumptions underlying educational theories and approaches, and their influence on (b) educational principles, (c) educational methods, (d) educational practices, and (e) student learning outcomes. I demonstrate that such a multi-level analysis is essential both to (a) identify the specificities, divergences, and convergences between existing educational theories and approaches and (b) to critically analyze them, notably by assessing the impact of their epistemological assumptions on student learning. In particular, I address and advance several fundamental debates in the educational sciences: (a) the constructivist-instructivist debate, (b) the divided field of research on conceptual change, and (c) debates regarding the influence of teachers’ epistemological beliefs on instructional practices. The thesis has also demonstrated (a) The problematic impact of empiricist assumptions on influential trends in school education, and (b) the need to investigate the influence of assumptions about concepts on instructional approaches in educational research.