Enfance - Année 1974 - Volume 27 - Numéro 3 - Pages 175-181An experiment borrowed from Piaget and Inhelder's researches (1952) has been given to children in special form (for school-maladjusted and retarded children) : their behaviours were of a concrete operational level and so they were of backwardness regarding their age. These subjects were trained in relation with the task in question plus verbal explanations. Two weeks later, a same kind of structural experiment was given to them but the material was different. None of the subjects were able to reach a formal level in their performance and this infered the hypothesis. On the other hand improvments could be ascertained but they are nevertheless of a concrete level. 7 pages Source : Persée ; Ministère de la jeunesse, de l’éducation nationale et de la recherche, Direction de l’enseignement supérieur, Sous-direction des bibliothèques et de la documentation.