Our research focuses on the processes of professional knowledge elaboration by physical education student trainees in an initial training system in France. This system combines classroom teaching situations and practice analysis situations, characterizing respectively the didactic and meta-didactic systems. The results reveal that, in their analyses, the student trainees jointly mobilize knowledge to be taught and for teaching, some of which are subject to a real co-elaboration supported by an evolution of their reflexive modalities. The discussion returns to the didactic and developmental stakes of the training situations at the articulation of the didactic and meta-didactic systems.