Abstract: Eight items of the cognitive tasks, which consisted of conservation(two-dimensional space, continuous quatity, weight, area, volume), classinclusion, multiplication of class and multiplication of relations, were usedto examine the same child of 7-yr-olds in the first grade of primary sch- ools for exploring the inter-intraindividual differences on the cognitive de-velopment. The results showed:1. The subjects have already mostly acquired the concepts of conservati-on (except the conservation of volume). The reasoning abilities for theclass inclusion and the logical relationship of the two-dimention developedrapidly.2. The interindividual differences of children for cognitive developmentdepended on the effects of interaction between the envirnment and activi-ties of the child. The schooling qualities, the educated levels of the par-ents and the level of intelligence of the child were the important variablesfor the individual cognitive development.3. The acquisition of the concepts which were assumed to belong to thesame cognitive structures was not synchronous. The phenomenon of hori-zontal decalage for the intraindividual cognitive development was explain-ed as the expression of the unstable state during the processes of acquiringrelevant concepts or abilities.

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