This study analyses the dynamics of the construction of agency and identity in one boy and one girl during the transitional period between primary and secondary school and the time when they embark on adolescence in a school in Colombia. Drawing from the principles of Grounded Theory, interviews and observations were conducted. The analysis applied a thematic and microgenetic analysis to identify issues in tension, functions, directions of change and dynamics of reflexivity and agency. The results showed a transformation of meanings and positionings in reflexivity on belonging to or being part of a social group at school, which mobilized the development of agency for both identifying and differentiating oneself. The agency<>reflexivity dynamics were articulated in identity construction processes in the midst of the challenges of school transitions and development. We discuss the findings and their implications in terms of changes and transformations to construct maps of agency development, as well as the possible discussions around the traditional Kantian educational models.