The view of scientific practice I rely on here is more sociocultural than cognitive. I borrow from theories of situated learning (Lave & Wenger, 1991) and cognitive apprenticeship (Collins, Brown, & Newman, 1989) the idea that learning science is an apprenticeship into ways of thinking. Such ways of thinking manifest themselves in the kinds of practices that students can engage in while they attempt to conduct authentic scientific inquiry. My interest here is therefore not to measure how much knowledge students might acquire through their inquiry, but to document how students construct meaning from data and how they view the relationship between data and possible interpretations of its meaning. The data that students select to include in explanations are likely to reflect their ideas about what data are important in understanding a particular natural phenomenon or event, what data are important to report in an explanation, and what data they feel like they understand. There is a complex entanglement here of students’ epistemic understanding of scientific explanation and argumentation and their conceptual understanding of particular domains, theories, and problem situations. One effort of this study is therefore to determine if students’ patterns of data citations in explanations to particular problems can help us to disentangle the influence of epistemic and conceptual understanding in students’ efforts to scientifically explain natural phenomena.