This paper aims to explicit the importance of the teacher as an agent of the mediation process in education, and how he conceives the teaching-and learning process in an action mediated in a classroom in Secondary School, with a reference to Vygotsky's works, to whom teaching and learning are connected, and also to Wertch and other authors as well. Five teachers who participated of this study answered to a semi-structured interview. The information was transcribed and constituted a corpus submitted to a content analysis. After that analysis, their conceptions were confronted with those of Vygotsky. Then, it was observed that, in the contemporary school, the action mediated is oriented exactly by the functions of the cultural tools, which shape the environment and the learning which is developed in it. And, in this process, the teacher has a fundamental role. The results indicate that, in the conception of the teachers, teaching-and-learning are the two sides of a same coin, and the teacher has a key role in promoting learning since he is the one who performs the pedagogical action. Then these teachers conceive teaching-and-learning in a completeness, weaving an own sense to the action mediated in the interaction with the student.