Scholars of language development have long been challenged to understand the development of functional categories. Traditionally, it was assumed that children's language development initially relies on lexical elements, while functional elements become accessible only at later periods; and that it is lexical growth which bootstraps grammatical…

This article reports on the development and use of the Developmental Sentence Scoring for Japanese (DSSJ), a new morpho-syntactical measure for Japanese constructed after the model of Lee's English Developmental Sentence Scoring model. Using this measure, the authors calculated DSSJ scores for 84 children divided into six age groups between 2;8…