Abstract: This is the second report on the investigation into development of concepts in children of 4—9 years of age.This study comprises two parts: the first aiming to investigate the developmental trends reflected in children's ability to classify, and the second concentrating on the age at which classification can be seen as a turning point in conceptual thinking.108 children of 4—9 years were each asked to sort objects depicted on cards, according to his or her own ideas of classification. Another 72 children in the age groups of 5, 5 1/2, and 6 performed the second part of the experiment.The results indicate:1) Children under 4 failed to carry out classification.2) Children of 5—6 years showed a rudimentary ability to classify but their classification was mainly on the perceptual level.3) Beyond 6—7 years, the children showed a conceptual ability in classification. Their conceptual thinking seemed to reach a new level.4) In children from 4—9 years old, the turning point from perceptual to conceptual thinking as reflected in ability to classify seemed to fall between the age of 5—6, and especially 5 1/2—6.

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