This contribution asks the mechanisms and effects going with pedagogical interaction. It puts in perspective the concepts of transmission, mediation and relations. Indeed, the pedagogical interaction isn't the enouncing of a discourse or the transmission of a knowledge. It's through the relationships between teacher and learners that get out some forms of communication. The retroaction facilitates the didactical exchanges when the metacommunication explains the knowledges. Finally, the retrotransmission underlines the part of the intersubjective communication in pedagogical frame.