This research investigates the use of polite form by elementary school students and factors influencing the use of polite form. Contained in the data are voice recordings of the interactions between the tester and 22 students from grades 2 through 6 utilizing DLA (Dialogic Language Assessment). The results indicate that while frequency of use differed among subjects, all students used a polite form that indicated formal act. Meanwhile, the polite form that indicates the speaker is regarded as high in social rank was observed in students who frequently use polite form. Language factors related to polite language usage such as complex syntax, the style used by the speaking partner, and fixed and idiomatic expressions, were included. However, it was indicated that there is no definite connection between the indexical meaning of the polite form and actual usage in terms of language knowledge possession.本研究は，2013年度JSPS 科研費25284096（基盤研究（B）『アーティキュレーションを保証する言語能力アセスメント実施支援システムの構築』研究代表者：渡部倫子）の助成を受けたものである。