This study analyzes how a teacher in the United States used systemic functional linguistics to design a blog-mediated writing curriculum to support second grade English language learners' (ELLs) literacy development and abilities to use computer-mediated communication tools for social and academic purposes in and out of school. The questions posed by this study relate to how blogging practices shaped a focus student's emergent uses of print over nearly two years in a U. S. urban school serving a large Puerto Rican community. This study is informed by Halliday's theory of systemic functional linguistics (SFL) and Vygotskian conceptions of appropriation and mediation. Using a combination of ethnographic methods and the tools of genre analysis, the findings indicate that blog-mediated writing practices afforded students an expanded audience and range of purposes for literacy activities. These practices, coupled with genre-based instruction, supported the focal student's emergent literacy development. The implications of this study relate to conceptualizing how ideational, interpersonal, and textual metafunctions of language intersect through computer-mediated communication to support L2 language development.