Abstract: A study was made among kindergarden children of 4-7 years in Beijing.Each child was asked to do some tasks on class inclusion and number inclusion.The results show that: 1. In general, the successful performance rises with increasing age for thethree different tasks. 2. Variations are shown in different age groups. In class inclusion, thegreatest development is shown in the age group 5, 5-6, while in number inclusionit is around tbe age of 4-5. 3. Children's responses shown in the course of experiment can be classifiedas of three different levels. At the first level, children can not see the relationbetween part and whole. During the second level, they make increasing correctresponses through representation. At the third level, they perform the tasknearly without mistake, showing full comprehension and some understanding oflogical relationship.

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