Abstract: This study is based on an experiment conducted among a number of Zang (Tibetan) and Hun children of 5—11 years of age on the Qinghai Plateau. They were asked to compare the lengths of two or three objects to examine the stability of their concept of length. The results indicate:(1) The stability of their concept of length increased with age. There were no significant differences in the performances of Zang and Han children within the age groups of 10 and under; significant differences occurred only in the 11-year-old age group. The ages of 7,9 and 10 were turning points which deserved particular attention; (2) The development of the stability of the children's concept of length underwent four stages roughly corresponding to their ages, but there was no clear-cut transition from one stage to another. The development is the result of interdependence and interaction between various cognitive factors; (3) The "conservation" of concept is a complex and changeable process. The results of the study show that the relations between direct and indirect cognition were important factors in the formation and development of the children's cognitive structure; (4) Differences in cultural and educational backgrounds definitely influenced the development of the stability of their concept of length.

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