Abstract: Four items of logical cognition tasks, which consisted of volume conservation, class inclusion, multiplication of class and multiplication of relations,were used to examine the same children of 7-yr-olds,9-yr-olds and 12-yrolds in primary schools for exploring the age differences, inter-intra-individual differences on the cognitive development. The results showed:(1)The results of the cross-section and longitudinal studies showed consistently that achievement of cognition advanced with age.(2)The interindividual differences of children for cognitive development was effected by the schooling quailities,the educated level of the parents and the level of intellgence of the child.(3)The acquisition of the concepts which were assumed to belong to the same cognitive structure was not synchronous. The children′s cognitive development doesn′t change according to a fixed order-from simple to complex.

Key words: Logical relationship, Cognitive development, Interindividual differences, Intraindividual differences