On the writing component of the most recent National Assessment of Educational Progress, 12th grade high school students' scores on argumentative tasks were lower than on tasks that required them to explain or to convey an experience ("National Assessment of Educational Progress," 2011). Similarly, 11th and 12th graders at the research site for this study have struggled most with writing tasks that require them to integrate sources into an argument about an issue of public discourse. In response to these challenges, this quasi-experimental study investigated the effect of classroom discourse on argumentative writing among English language arts students in 11th and 12th grades in a Boston public high school. Unlike previous work in this area, this study (1) focused on high school upperclassmen in English classes, (2) used a standardized assessment tool designed by the College Board to measure growth in argumentative writing, and (3) provided descriptions of the discourse interventions to be followed by classroom teachers, which could later be implemented by other teachers outside of the study. At the conclusion of the study, the estimated marginal mean on a College Board assessment of argumentative writing for students who experienced discourse where teachers focused on linking ideas and pressing for reasoning (M = 3.90, SD = 1.40) was significantly higher than for students who experienced procedural facilitation where teachers encouraged discursive interactions but did not explicitly prompt students to articulate their reasoning or to link their ideas to those of others (M = 3.32, SD = 1.43), F(1, 112) = 8.056, p = 0.005, partial eta squared = 0.067. These results provide confirming evidence for sociocognitive learning theory and help fill gaps in the literature as suggested above. In addition, the present study has helped to confirm linking ideas and pressing for reasoning as discourse moves related to improvements in argumentative writing. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]