How do classroom exchanges shape the developing forms and functions of literacy learning and teaching as students transition across the years of schooling? We explore this question using excerpts from literacy lessons from primary and secondary classrooms, showing how lesson exchanges develop as trajectories connecting different forms of 'knowing' and 'doing' literacy as a meaning making, socially grounded action. In this article, we refer to transitions as the movements between place and time, and trajectories to refer to developmental progressions. We identify a variety of interactional moves that in lessons shift students' attention to different facets of literacy learning, shuttling across material, social, cultural and disciplinary considerations, allowing the gradual functional connections between these dimensions of literacy to emerge and become routine. We show that these moves, whether sudden or gradual, remarked on or not, largely depend on how a teacher scaffolds the work interactionally, then-and-there, in the lesson. Drawing on Conversation Analysis we examine the details of selected classroom transcripts from recorded primary and secondary lessons. We show the emergence of literacy's changing shape and significance (emerging as literacy trajectories), and we suggest what these changes might signify subsequent developments in students' literacy learning as participants in pedagogical interactions. Our exhibits indicate that the emergence of literacy trajectories can be productively reconsidered in terms of Vygotsky's (1978) notion of changes over time in the interfunctional relations among learning processes (e.g., 'remembering'-'thinking') and the focus of literacy lessons (e.g., 'vocabulary' and 'meaning'). We discuss how these interfunctional relations are signaled and made relevant in classroom exchanges.