Drama is used to build knowledge and understanding in science as part of a socio-linguistic, constructivist approach. Role-plays, where learners act as analogues for components and processes, help access abstract ideas. However, a problem restricting many science teachers using these approaches has been that they lack sufficient pedagogical knowledge of drama. Our question was, therefore, to what extent do student teachers who are science majors make the necessary "pedagogical border crossings" from drama into their personal pedagogies for science? We observed and recorded the lessons of six volunteers who taught science using drama in grade 7. Our analysis of lesson features that are critical for successful outcomes, based on an adapted version of Tripp's critical incident method, and student teacher interviews show that role-plays can be powerful border-crossing objects between science and the arts. Findings show that some development is needed to link learners' actions to concepts and provide more suitable analogues and sufficient learner autonomy. We see drama as an important tool in science teaching and suggest conditions necessary for the initial training of science teachers that could make them better users of drama as role-play to teach science.