This study carries out an analysis of the tacit or informal influences that teachers have on their students both trough the way they are an the way they act in the daily dynamics characteristic of ordinary teaching. It shows how, in ahidden, latent and subliminal way, in the thousand and one daily interactions, the teacher contributes strongly to the development of the basic moral personality of his students.
An example of this informal moral education is given in a practical case taken from the observations of a woman mathemathics teacher during a series of classes. Finally, it is strongly suggested that the data analysed should contribute to awaken the professional conscience of teacher in order to form a moral responsability in them that qualifies them for to be reflexive and morally competent as regards their specific educational and educating tasks.
Key words: Moral education. Tacit knowledge. Teacher's moral influence. Informal education. Professsional ethics.