Video-based classroom research is opening-up exciting new insights into how teachers generate productive opportunities for student engagement in quality learning. This research reveals the extent to which effective teachers draw on a range of multimodal representations of science phenomena and learners must use these as semiotic resources for learning. This case study of a Year 4 class studying an introductory astronomy unit offers insights into a teacher's orchestration of a range of multimodal representations to support the co-construction of an explanation for a science phenomenon.