In application of the law of February 2005, many teachers have been brought to host within their mainstream class a disabled child. Although the problems concerning inclusion are mainly approached within the different fields of research from the point of view of the pupil, our approach focuses on the work activity of the teacher. In order to analyze the activity of teachers, we set up an observation ground in three primary schools during three consecutive years. We were thus able to observe the different kinds of resources brought into play by six teachers faced with the presence of a disabled pupil in their class and to show that, despite the child’s difference and the lack of prescription concerning what to do; they developed efficient and dynamic teaching. The presence of a disabled child in a mainstream class serves as a magnifying glass for research in ergonomics and reveals that in supposedly “extra-ordinary” situations, teachers in fact appropriate and expand ordinary techniques already available in the professional genre.