The WAI is a technique for investigating self-attitudes invented by Kuhn  McPartland (1954). In this technique, subjects write twenty statements responding to a question "Who am I? It is effective for investigating self-image because it allows each subject to describe himself/herself in his/her own words. However, to analyse WAI responses statistically, they must be classified into some categories. "KIJUNSHO" is a system of categories for WAI responses constructed through content analysis of the responses. And it have been revised four times. In this study, the WAI responses of 4,948 subjects aged from 9 to 19 are classified by using "KIJUNSHO". Then, the development of self-image is investigated based upon the analysis of the WAI responses. The results show that large part of WAI responses are self-images about one's directive aspect of personality or one's social relation. Self-images about one's need, hope or desire and self-images about one's character are found frequently among older subjects' responses. The proportion of subjects whose responses are classified into social or abstract categories is higher in older subjects than in younger subjects. These results mean that self-images of older subjects are more internal, more social, and more abstract than those of younger.