The present paper examines 196 Korean narrratives of three age groups-6-year-olds, 11-year-olds, and adults-and explores three research questions about the intersentential '-yo', which seems to show up in children's spoken utterances temporarily in their language development: (1) What are its functions in discourse? (2) where does it come from? and lastly, (3) what is its distribution in discourse? In the experiment, a total of 196 Korean children and adults were each asked to tell a brief story while looking at a series of pictures in accordance with a given title. The results show that the intersentential particle '-yo' seems to appear in children's discourse after the acquisition of the politeness sentential ending '-yo', and suggest that the intersentential '-yo' might be historically derived from the sentential ending '-yo'. This study also shows that there is a hierarchy non-final marker > subject > object > oblique in the easiness of which element '-yo' should be attached to. Finally, this study claims that, although the intersentential '-yo' starts as a filler giving the speaker time to plan ahead, it develops as a topic introducer at a later stage.