In this study we video-filmed upper-secondary physics students working with a laboratory task designed to help them learn about the Earth’s magnetic field. Students worked in pairs with a hand-held magnetometer to determine the direction of the Earth’s magnetic field. As the magnetometer is moved, the x, y and z components of the Earth’s magnetic field are displayed on a computer screen. The students were simply instructed to find the direction of the Earth’s magnetic field and mark this direction using a red paper arrow. A full multimodal transcription of the student interaction was made. In our analysis the central role of transduction (defined as the movement of semiotic material from one mode or semiotic system to another) became clear. Three separate transductions of meaning were identified. The first—transduction of the meaning potential in the room to the computer screen by themagnetometer—allowed students to interact with the invisible magnetic field. Then, as the students worked together, their coordination of resources was transducted to the red paper arrow. This allowed the students to display the results of their work in a persistent representation. The arrow then functioned as a coordinating hub for the final discussion, which resulted in transductionof meaning into student gestures. We suggest that this final transduction offers the possibility for teachers to check student learning. In conclusion, we recommend that teachers should think carefully about the resources provided in a task and the transductions that are expected to occur. The selection of a persistent resource as a coordinating hub may be useful. We also suggest that teachers should look for student transductions in their classrooms as confirmation that learning is taking place. In our analysis, when teachers noticed such transductions this often led to fruitful teacher/student discussions about the phenomenon at hand.