My aim in this paper is to show the relevance of an "effective semiotics"; that is, a field study based upon Peirce's semiotics. The general context of this investigation is educational semiotics rather than semiotics of teaching: I am concerned with a general approach of educational processes, not with skills and curricula. My paper is grounded in a field study that I carried out in a school, L'Ecole de la Neuville, implementing Institutional Pedagogy in France. I first investigate the relevance of Peirce's semiotics in such a context. I then propose several definitions for the word "institution", referring to the core concepts of this particular pedagogy, before describing the concept of "institution-sign", which is considered a useful tool for making effective connections between several aspects of semiotics. I finally assert that an institution constitutes a tool that allows teachers to favour semiosis in educational contexts.