High-quality classroom dialogues improve students' capacities to learn school subjects and help them develop more general skills such as collaboration and critical thinking. In this chapter, we take a sociocultural stance toward learning and cognition. "Gap-closing" is used as a key concept to understand and explain why and how teachers and students interact in order to advance students' agency. To effectively enhance classroom dialogues, teachers need to use language in specific ways, which can be supported by digital tools like Talkwall. Talkwall is a web-based micro-blogging tool that enables students to send short text messages during classroom discussions with their tablets or mobile phones. Their contributions are then shared and represented visually; the developing ideas are connected in a digital representation that participants can continually refer to throughout the dialogue, keeping each idea present and available for the whole class. Talkwall is designed to support the movement of classroom dialogues between teacher-led, whole-class discussions and small, student-group discussions. The empirical illustration used in this chapter is based on an interaction analysis of how students and teachers use rap lyrics to learn literary methods and concepts. [For the complete volume, "Designs for Experimentation and Inquiry: Approaching Learning and Knowing in Digital Transformation. New Perspectives on Learning and Instruction," see ED661573.]