Rich classroom discussion, or discourse, has long been a recommended pedagogical practice in K-12 math and science education. Research shows that discourse is beneficial for all learners, but especially for English learners and minoritized students in STEM. Discourse helps develop students' agency, academic language, and conceptual understanding. Some K-12 computer science (CS) curricula incorporate student discourse, but we believe it is under-used. In this paper, we review how discourse helps students learn, discuss the use of discourse in CS and math education, share ideas for promoting discourse in CS classrooms, and call on curriculum developers, teacher professional learning providers, and researchers to support the increased use of discourse in K-12 CS education.