Existing research on students' conceptions contain competing philosophical positions concerning the nature of students' ideas--whether those ideas are coherent, systematic and theory-like, or fragmented and incoherent. Existing research has also focused primarily on studies of individual conceptions rather than investigating multiple, related conceptions. Nevertheless, there is wide agreement among researchers and teachers alike that the ideas students bring to a learning situation are fertile ground for investigation, and that students' ideas should be taken into consideration when planning science instruction. The purpose of this study was to examine the representational, conceptual framework, and contextual consistency aspects of two students' ideas across concepts of evaporation, condensation, and boiling. Knowing the consistency students express for each specific concept, and how well they integrate these related concepts, would offer insights that could potentially impact student learning. We present two case studies here that highlight the degree of consistency expressed by two students across different representations for each target concept and in instances where these conceptions are related to one another. Findings from this study highlight the need for attention to the consistency of students' ideas across multiple, related concepts. Implications from this study support our recommendation for metaconceptual teaching strategies that would help students examine different representations for the same concept and also to examine the consistency of their ideas across multiple conceptions.