This study fits into a dual paradigm: i) studies on the acquisition of written production which analyze, in a complementary way, the contexts of teaching, pupils’ written produc-tion, the related verbal explanations and the effects of feedback on the written production; ii) current research on analyzing teaching practices, integrating the various variables related to the teaching situations and, more particularly, analyzing learning interactions. Invented writing fits into these paradigms and integrates the linguistic and didactical factors, as well as the contextual parameters. To assess differential teaching practices, two first-grade teachers were monitored during a school year: one regularly includes invented writing sessions, the other does not. The transcriptions of three video sessions of teaching writing, recorded at the beginning, middle and end of the school year, provide a quantita-tive and qualitative analysis, focused on general educational determinants and on didacti-cal determiners specific to the purpose of learning. The aim is, as such, to accurately assess the didactical processes implemented, their efficiency in terms of learning, the effects on pupils’ acquisition of the alphabetical principle, and in addition, on their func-tional command of the French writing system.