Purpose: Study on the development of children's thinking on causal relations of natural phenomena is necessary-at least to respond to the demands made by scientific education theories. As a first step of experimental study on the subject in qeustion, we tried to find out how children understand causal relationships of demonstrable natural phenomena.
Method: We made eight problems including eleven demonstrable questions in the field of physics and chemistry. To get exact answer, we interviewed the
subjects individually and gave questions orally. Subjects: Ten boys and 10 girls each from the 3rd grade of Kakogawa Elementary School, and the 1st grade and 2nd grade of Kakogawa Junior High School. Total 120 pupils.
Arrangements of Result: Children's explanations were classified into five categories. The five categories were given grade points based upon their logical perfectness and age distribution. Then the developmental curve was observed. Sex differences were also observed.
Conclusion: (1) When children's level of understanding of causal relationship was low, the explanation were illogical and were based upon inpressions of things used in demonstration or fragmental phenmena. However, as their level of understanding went higher, the logical explanations became possible. Because the modes of explanation were different among children of the same grade, depending on the questions, we cannot conclude that a certain from of explanation corresponds to a certain grade.
(2) Sudden decrease of illogical explanations and increase in logical ones was found between the 5th grade of the elementary school and the 1st grade of the junior high school. Change in the quality of thinking from understanding of material causal relationship to that of abstract causal relationship takes place during this period.
(3) Generally speaking, girls are inferior to boys, especially at the 3rd grade-when understanding of material relationships is complete among boys and at the 1st grade of junior high school-when understanding of abstract relationships begins to be complete.