This article reports on findings from the first year of a professional learning partnership aimed at supporting elementary teachers in improving their writing instruction for emergent bilingual students. Specifically, we present a case study of one fourth grade teacher's writing instruction, exploring how an introduction to a functional approach to teaching argument writing contributed to shifts in practice and in her understanding of effective writing instruction for emergent bilingual students. The research team engaged in two cycles of data collection across 5 months, conducted before and after an introductory seven-hour professional development workshop on systemic functional linguistics (SFL) genre pedagogy, in order to document changes in how the focal teacher was enacting and conceptualizing writing instruction for emergent bilinguals. Findings revealed three central shifts in the teacher's writing instruction: (1) from surface-level genre engagement to exploring functional relationships between genre stages, (2) from assessment-oriented writing instruction to learning activities grounded in authentic purpose and audience, and (3) from general language supports to targeted, contextualized writing scaffolds. This study builds upon existing scholarship by illustrating the potential of (even limited exposure to) SFL genre pedagogy to shift teachers' writing instruction toward social semiotic perspectives of language and literacy. We also extend existing research by interrogating the institutional and ideological challenges teachers encounter when taking up SFL genre pedagogy and by offering some initial insights into the potential for engaging in SFL genre pedagogy in bilingual learning spaces.