This study investigates representational code-switching (RCS) by considering three high school students' communications in the process of comparing and contrasting pairs of representations (e.g., equation and graph) in the context of rational functions. Supporting this study is research in the realms of students interacting with mathematical representations, practicing language learning, and linguistic code-switching (LCS). Attention is given to assessing student mathematical understanding based on frequency and type of RCS performed. This investigation concludes that RCS demonstrates either weaker or stronger mathematical performance depending on whether the RCS evidences semantic elaboration, isomorphic and transcendent connections, and domain register knowledge.