Flourishing in today's global society requires citizens that are both intelligent consumers and producers of scientific understanding. Indeed, the modern world is facing ever‐more complex problems that require innovative ways of thinking about, around, and with science. As numerous educational stakeholders have suggested, such skills and abilities are not innate and must, therefore, be taught (e.g., McNeill & Krajcik, Journal of Research in Science Teaching, 45(1), 53–78. 2008). However, such instruction requires a fundamental shift in science pedagogy so as to foster knowledge and practices like deep, conceptual understanding, model‐based reasoning, and oral and written argumentation where scientific evidence is evaluated (National Research Council, Next Generation Science Standards: For States, by States, Washington, DC: The National Academies Press, 2013). The purpose of our quasi‐experimental study was to examine the effectiveness of Quality Talk Science, a professional development model and intervention, in fostering changes in teachers’ and students’ discourse practices as well as their conceptual understanding and scientific argumentation. Findings revealed treatment teachers’ and students’ discourse practices better reflected critical‐analytic thinking and argumentation at posttest relative to comparison classrooms. Similarly, at posttest treatment students produced stronger written scientific arguments than comparison students. Students’ growth in conceptual understanding was nonsignificant. These findings suggest discourse interventions such as Quality Talk Science can improve high‐school students’ ability to engage in scientific argumentation.