Despite the documented need to train and educate more cybersecurity professionals, we have little rigorous evidence to inform educators on effective ways to engage, educate, or retain cybersecurity students. To begin addressing this gap in our knowledge, we are conducting a series of think-aloud interviews with cybersecurity students to study how students reason about core cybersecurity concepts. We have recruited these students from three diverse institutions: University of Maryland, Baltimore County, Prince George's Community College, and Bowie State University. During these interviews, students grapple with security scenarios designed to probe student understanding of cybersecurity, especially adversarial thinking. We are analyzing student statements using a structured qualitative method, novice-led paired thematic analysis, to document student misconceptions and problematic reasonings. We intend to use these findings to develop Cybersecurity Assessment Tools that can help us assess the effectiveness of pedagogies. These findings can also inform the development of curricula, learning exercises, and other educational materials and policies.