Science education has long seen an emphasis on supporting students' epistemological understandings of how scientific knowledge is constructed and evaluated with the expectation that these understandings will support the students' own construction and evaluation of scientific knowledge. However, research has shown that this connection does not always bear out because the assumption does not attend to the context in which students' epistemological understandings are accessed. This study presents a microgenetic analysis of two students' model-construction endeavor to explore how context-sensitive analyses influence our characterization of a student's epistemological sophistication. In this analysis, we show that both students held a target epistemological resource but that they did not apply this resource to their final model design consistently. In addition, we show that one student articulated why she applied one epistemological resource instead of the other while the other student did not. We use this case study to explore possible definitions of epistemological sophistication. We conclude that evaluations of epistemological sophistication should focus on the ways in which students discuss their epistemological decisions rather than on the epistemological underpinnings of their knowledge construction work. We conclude with implications for instruction.