Abstract: The purpose of this study is to explore the developmental levels of 8-15-year-old children's concept of intersection set and the process of their resolving inter-section problems,analysing the interaction of various components in children'scognition.151 subjects were tested with three intersection problems in differentdegrees of difficulty,presented through words,pictures and physical objects. As the results suggested:Primary school pupils had the mental factorsfor mastering simple intersection sets.In the cognition of intersection by 8-15-year-old children there exists interaction of concepts,images and sensori-motor manipulations,and the latter two play an important role in it.Theprocess of resolving intersection problems is an active one:the subjects ponderactively,make strategy,and form related concepts by the help of picturesand manual manipulations.

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