Inspired by Jean Piaget, he has inflected the latter’s theoretical framework, highlighting the importance of learning contents in development and the role of mediation. This led him to Lev Vygotski, but with the aim of synthesis rather than confrontation. What strikes one most about his work is that it shows, through acts, how developmental psychology contributes to the development of psychology itself. What greater homage could a pupil pay to the Genevan master?