Integrating reading and writing instruction with scientific inquiry can enhance student learning, yet the nature of the connections between each of these learning domains remain underexplored. In this systematic review, we analysed 16 interventions in elementary education in order to develop a categorization of the functions of reading and writing within scientific inquiry. Inductive analysis resulted in three main categories of functionalities: reading and writing as support for understanding, doing, and concluding in scientific inquiry. Specific functions belonging to each category are identified and illustrated with learning activities as described in the interventions. These functions highlight a range of possibilities, informing researchers and practitioners about aligning reading and writing with scientific inquiry. The review also included a deductive analysis of instructional reading and writing support in these interventions. Findings revealed that support was minimally described, primarily consisting of explanations (including direct instructions and examples) and providing graphic organizers (e.g., worksheets with prompts). Support for reading activities focused mainly on general and disciplinary-specific strategies for reading comprehension. Writing support emphasized disciplinary-specific strategies such as writing according to an argumentation structure, preparing scientific explanations, and documenting data. The results of this study advance our understanding of the rationale for integrating reading, writing, and scientific inquiry and can inform future integrated interventions. It also underscores the missed opportunities and gaps in current interventions regarding the interactions between reading, writing and scientific inquiry in elementary education.