||Lee, In. (2017). Development of two young Korean learners' English grammar: A one-year-long case study. The Linguistic Association of Korea Journal, 25(3), 25-50. The purpose of this study was to find out how young Korean learners of English developed their English grammar. One boy in G6 and his sister in G4 were selected as language informants. Their spontaneous utterances were collected for one year from February 2015 to January 2016, at intervals of a month, and analyzed with respect to the following criteria: (i) the total number of Tokens, (ii) the total number of Analysis of Speech units (AS-units), (iii) changes in the use of NPs and VPs, and (iv) changes in the use of AS-units. To trace each informants developmental process, NPs and VPs s/he used at three points were classified as well-formed or ill-formed while AS-units were grouped into three: well-formed, ill-formed, and incomplete. The analysis of their spontaneous utterances showed that both learners English grammar improved not only quantitatively, but also qualitatively. Especially, the girls grammar remarkably improved.