Abstract: This study is aimed at 1st and 3rd year students of junior high schools and 2nd year students of senior high schools. The results are:1. The age-characters of thinking development are: Formal logical thinking begins to prevail in the 1st year of junior high and tends to mature by the 2nd year of senior high. Dialectical logical thinking emerges in its initial form in the 1st year of junior high and begins to take hold in the 2nd year of senior high.2. The character of thinking development of adolescent students of both sexes are: The over-all level of thinking development is about the same in boys and girls, though both have their own characteristics. The idea that "boys are superior to girls" or vice versa is not accepted.3. There are differences in the development levels of student sthinking between different types of high schools.

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