The idea of elementary school students working together on mathematical tasks is not new, but recent attention to creating purposeful discourse in mathematics classrooms prompts teachers to revisit discourse-promoting strategies for mathematics lessons. The Common Core's Standards for Mathematical Practice (CCSSI 2010) encourage teachers to foster opportunities for students to make conjectures, analyze situations, and create and argue solutions with one another. The type of purposeful discourse that promotes these behaviors supports the development of students' conceptual understanding (NRC 2001) around high cognitive-demand tasks (Smith and Stein 1998). However, facilitating this type of discourse is no easy feat. How can teachers implement a lesson that promotes purposeful mathematical discourse? In this article, the authors focus on the beginning of a lesson that is organized around a high-demand task; that is, they focus on the launch phase of the lesson, when the teacher is getting students ready to work on the task.