There is much agreement among chemical education researchers that expertise in chemistry depends in part on the ability to coordinate understanding of phenomena on three levels: macroscopic (observable), sub-microscopic (atoms, molecules, and ions) and symbolic (chemical equations, graphs, etc.). We hypothesize this "level-coordination ability" is related to the formation and use of principle-based, vs. context-bound, internal representations or schemas. Here we describe the development, initial validation, and use of a card sort task to measure the level-coordinating ability of individuals with varying degrees of preparation in chemistry. We have also developed a novel method for generating two-dimensional sorting coordinates which were used to arrange participants along a hypothetical progression of level-coordination ability. Our findings suggest the card sort task shows promise as a tool to assess level-coordination ability. With the exception of graduate students, participant groups on average progressed from sorting by level of representation toward sorting by underlying principle. Graduate students unexpectedly sorted primarily by level of representation. We use these data to form initial hypotheses about a typical process for the development of level-coordination ability and schema formation. In doing so, we demonstrate the usefulness of our task paired with sorting coordinate analysis as a tool to explore the space between novice and expert behavior. Finally, we suggest potential uses for the task as a formative assessment tool at the classroom and program levels.