Discipline: Education
The study investigates the development patterns of the operational thinking of school children longitudinally assessed at ages 7, 9, and 12 (ti.= 80) on four cognitive tasks: Class inclusion, Multiplication of classes, Multiplication of relations, and Conservation of Volume. A horizontal decalage and vertical decalage for the acquisition were found. Concrete reasoning was manifested in some general stage like manner combined with individual variations. A phenomenon of error of growth was identified in the process of acquiring conservation of volume. The inter-individual differences in development was constrained by the interaction of internal factors (e.g., age, learning ability, level of intelligence) and external factors (e.g., the qualities of schooling and family education). Low level-ability children gained more benefits from schooling.