Abstract
This paper presents a synthesis of several studies conducted about the construction of learning inequalities in mathematics classrooms at the beginning of secondary school in France. These studies were conducted within a framework inspired by Activity Theory, applied to the process of mathematics teaching and learning in school. This synthesis highlights on one hand the role played by students themselves and their characteristics in the differentiation and, on the other hand, the role of the transparency for teachers of some aspects of what happens in classrooms in the construction of learning inequalities. These results allow (re-)discussing the relevance of the categories of active differentiation and passive differentiation identified in research in sociology of education about learning inequalities. It also shows that studying the process that leads to learning inequalities within the classrooms necessitates a conception of teaching practices that encompasses not only the complexity of the constraints but also the issues related to knowledge (i.e. issues with a didactical nature), especially when it comes to consider alternatives and conditions for their implementation.