This text addresses the schooling of children and adolescents with serious developmental impairment or atypical structuring, such as autism or psychosis. The perspective adopted builds on Freudian-Lacanian psychoanalysis, philosophical hermeneutics, special education, and processes of inclusion. More specifically, it reflects on the place of diagnosis in the construction of (im)possibilities within schools, based on an analysis of academic and scientific production on the theme over the past 28 years. The existience of a centrality of diagnosis is proposed, in the establishment of educational pathways for these subjects. Diagnosis is often identified as an act of unveiling and/or decoding. From another perspective, it is defended that the relationship between diagnosis and schooling involves the construction of a reading and the invention of possibilities. As there is no pre-established path, guaranteed and anticipated by the diagnosis, the teacher and the school are responsible for their choices, seeking to enhance the school experience of their students. The basis of their action is therefore ethical conduct, rather than a method or technique.