This research consists of three parts : (1) the analysis of error responses of teacher-made tests, (2) the analysis of scientific knowledge from the point of view of its developmental aspect and (3) the analysis of the retention of scientific knowledge from the point of view of its contents. Each part will be explained in detail as follows : (1) Fifteen problems referred to "science of water" were selected from various teacher-made problems. Errors to all' items of the problems were classified into the several degrees from trifling degree to serious degree, according to the distance from correct response, and scored as -1, -3, -3, etc. , As the results, many sorts ,and various degrees of errors were revealed. In comparison of the rate of errors, the rate of non-response and the average minus scores of a error between the pupils who were good in science and those were poor, the good pupils tended to get correct response and even if they mistake, they made only trifling errors. The pupils on the medium made various degrees of errors, some of them relatively trifling but some considerably serious or unusual. Many poor pupils had no response or made so serious errors that we could not find out the relationship to the correct response at all. (2) The processes in which the scientific concepts developed were considered as follows.