In the STEM fields, adequate proficiency in reading and interpreting graphs is widely held as a central element for scientific literacy given the importance of data visualizations to succinctly present complex information. Although prior research espouses methods to improve graphing proficiencies, there is little understanding about when and how students develop these skills during the course of their education. To address this gap in the research, we sought to create an assessment tool to measure differences in these abilities across groups with varied levels of experience in science, technology, engineering, and mathematics. This study presents results from a data visualization literacy assessment we created to begin to understand the development of expertise in this domain.