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Abstract: In the development of the number concept and operational ability ofschoolchildren, factors of age characteristics, critical period, and the unityof stability and variability of age characteristics are demonstrated. Theauthor has advanced some new ideas for the structure of thinking, andbelieves that the structure of thinking is a system which has certainmaterials, direction and form under the control of adequate principles. Thedevelopmental trend of the thinking structure in schoolchildren was alsostudied in this article.

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