To function effectively as a learning environment, a simulation system must present learners with situations in which they use relevant knowledge, skills, and abilities. To function effectively as an assessment, such a system must additionally be able to evoke and interpret observable evidence about targeted knowledge in a manner that is principled, defensible, and fitting to the purpose at hand (e.g. licensure, achievement testing, coached practice). This article concerns an evidence-centered approach to designing a computer-based performance assessment of problem solving. The application is a prototype licensure test, with supplementary feedback, for prospective use in the field of dental hygiene. We describe a cognitive task analysis designed to: (1) tap the knowledge hygienists use when they assess patients, plan treatments, and monitor progress; and (2) elicit behaviors that manifest this knowledge. After summarizing the results of the analysis, we discuss implications for designing student models, evidentiary structures, task frameworks, and simulation capabilities required for the proposed assessment.