Science educators now broadly recognize the multimodal nature of learning in science, where learners make meanings within modes (linguistic, mathematical, visual, and actional) by using the conventions of different sign systems or grammars in these modes. However, how teachers guide students to link and infer new meanings across modes, called "transduction" (Kress & Van Leeuwen, 2006. Reading images: The grammar of visual design. Routledge, p. 39), is less clear. This mapping of meanings across modes through realizing, generating, aligning, and coordinating meanings in representations is crucial to learning and communicating scientific concepts, inquiry processes, and reasoning. In this paper we propose a pragmatist account of how young students can be guided to achieve cohesion in this process. Drawing mainly on Peirce's (1998, The essential Peirce: Selected philosophical writings. Indiana University Press) theory of sign functions and affordances, we describe how, in practice, transduction entails a sequence of meaning-making steps across and within sign systems. For Peirce, sign systems in science enable inferential meaning-making within modes, but signs within these grammars can also prompt, support, and confirm meanings across modes. We analyze student learning in an elementary school astronomy class to identify how transduction is enacted and supported. We draw on micro-ethnographic analysis of the teacher's interactions with students and their artifacts to identify key transduction enablers. We found that young students can engage successfully in trans-modal reasoning if multiple conditions are met, with implications for science inquiry design in general and the teacher's key role in transduction guidance.