The purpose of this paper is to clarify how the idea of a child's gender among the middle class has changed by analyzing "Eisaishinshi", a contribution magazine for children during the Meiji Era whose publication started before the practice of gender specification. This magazine was particularly chosen due to the fact that in modern Japan, the magazine used as supplementary materials in school education have also carried out sex specification at the time when the concept of gender studies in middle school education was put into practice in 1879. The results of the analysis are as follows. From 1877 to 1882, when "Eisaishinshi" was first published, children's compositions praised the merits of studying to attain careers and abilities. Their works also represented both the boy and the girl as "Shonen (the Youth)" based on the idea that they should have the same opportunity, which perfectly reflected the meritocracy society and civilization. However, since 1882, attention has been paid to the so-called "difference in intellectual power" between men and women. This led to the separation of "Shojo (the girl)" from "Shonen (the youth)", considering that the former has different opportunity from the latter, and to the emergence of different entities "Shonen (the boy)" and "Shojo (the girl)". This transition derived from the system of the study according to sex, by which the so-called" difference between men's intellectual power and that of women" has been realized. Two things have become visible from such a transition. Firstly, the transition has demonstrated two sides of the meritocracy by learning. The ideology, on the one hand, has supported a new image for women during the 1870s and the 1880s who pursued careers through studies. On the other hand, however, it has inevitably revealed the difference in intellectual power between men and women and justified gender discrimination as a by product of this difference. Consequently, since the practice of the study according to sex, the latter idea has been strongly influenced. Secondly, it has become clear that meritocracy has created two separate entities "Shonen (the boy)"and "Shojo (the girl)'. That is, females whose education and subsequent career have been severed in relation since study according to sex, have lost continuity between their way of life as "the mother", and that as "the girl". Unlike the boyhood which has been positioned as a preparatory period for the adulthood, the girlhood has been regarded as a specific time which will be completed in itself. In conclusion, the analysis has shown that the construction of a child's gender in modernJapan has been strongly connected with the meritocracy by learning that appeared at the time.