Literacy instruction in the 21st century must bolster students' ability to critically process text and craft well-reasoned written argumentation. The authors investigated changes in fourth-grade students' (N = 28; 15 girls) written argumentation as they used a researcher-developed graphic organizer (i.e., Quality Talk graphic organizer [QT[subscript GO]]). The authors also examined the extent to which students' graphic organizer performance predicted their written argumentation and whether such prediction was sustained across genres. Both QT[subscript GO] responses and written argumentation essays were scored for quantity and quality. Multilevel modeling analyses reveal that (a) both quantity and quality of students' written argumentation essays statistically significantly improved after students used QT[subscript GO] and (b) students' graphic organizer performance seemed to attenuate the effect of genre on their written argumentation for both quantity and quality. Results suggest that QT[subscript GO] facilitated students' written argumentation, making it easier for fourth-grade students to write about both narrative and expository texts.