Background: Vygotsky's theory of the internalization of signs provided the basis for this study. Aims: This study tried to analyse the processes by which second-grade students internalize school rules. Sample: Ethnographic data were collected on 102 lessons in a second-grade class (6-8 years) during 1 year. This study focused on three lessons (ethnographic data completed by video-recordings, post-lesson interviews with the teacher, and re-transcriptions of the verbal interactions of the lessons and interviews). Method: The longitudinal observation data were broken down into discrete transactions, crossed with the recorded data, and analysed in a four-step procedure. Results: The results showed that the students' self-regulated actions (voluntary performance of prescribed actions) corresponded to the teacher's presentation of the rules, which was varied and personalized. She used explanation/justification, negotiation, persuasion, or imposition as a function of the situation and the students concerned. The results revealed: (a) Multiple actions of explanation/justification of the rules, negotiation and persuasion to the entire class, (b) Personalized actions of persuasion and rule imposition in instances of heteronomous actions by students, (c) Actions adjusted to the dynamics of the transactions. Conclusion: This study demonstrates how closely the actions of teacher and students are linked. More than a linear process of rules internalization, education looks like a co-construction of rules between teacher and students. These results can serve as a basis for the tools of teacher teaching.