The study sought to determine the effects of teacher-introduced multimodal representations and discourse on students' task engagement and scientific language during cooperative, inquiry-based science. The study involved eight Year 6 teachers in two conditions (four very effective teachers and four effective teachers) who taught two units of inquiry-based science across two school terms. The results show that the very effective teachers spent significantly more time engaged in using embodied representations to illustrate points or communicate information. They also spent significantly more time engaged in interrogating students' understandings and scaffolding and challenging their thinking than the effective teachers. In turn, the students in the very effective teachers' classes spent significantly more time on-task and used significantly more relevant basic and scientific language to explain the phenomena they were investigating than their peers in the effective teachers' classes. These are behaviours and language that are associated with successful learning in science.