Science reforms in national K-12 science education standards position engineering as a discipline that can be productively integrated into science curricula. This integrated approach presents science as foundational to engineering and engineering as a tool to contextualize and reinforce science ideas such that students come to develop understandings about the natural and engineered worlds. To better understand if integrating engineering into science classrooms achieves the promise described in national reforms, we explored how elementary school students came to understand what is expected of them when asked to engage in an integrated science and engineering unit and whether their understandings represent epistemologically productive ways of integrating the doing of science and engineering. For this purpose, we examined video recordings, transcripts, and classroom artifacts of tasks from a 9-week unit contextualized in an engineering challenge in which students engaged in activities to explore, design, and build simple circuits devices to develop explanations of energy movement in a circuit. Our findings suggest that an integrated approach may be more problematic than promising; while at times students took up integrated tasks as opportunities to wonder about, question, and explore materials that sparked their interest, their framing of the tasks did not align with the vision for integration called for in current reform documents.