This case study examined planning decisions made and challenges faced by an elementary teacher in a high-poverty urban district to promote students' adoption of social norms of interaction for scientific discourse. Through interviews, document analyses, and observations during a science unit, the findings indicated that the teacher's planning first involved creating a classroom climate whereby students felt safe to share their thinking. Next, she provided students with structures for interaction and strategies for discourse based on knowledge she acquired from professional development in evidence-based discourse. She also incorporated these dialogic practices in all subjects to extend student practice. The challenges in promoting scientific discourse included accountability pressure, inadequate resources, limited time, paucity of collegial collaboration, and student variability in discourse.