The purpose of this research was to examine the consistency between students' practical and formal understandings of scientific epistemologies (also known as nature of science (NOS) understandings) in the context of a research apprenticeship program. Six high school student participants of a residential summer research apprenticeship program at a major university in the southeastern USA were interviewed twice during their experience to elicit their perspectives regarding their practical epistemologies. A phenomenological approach was used to analyze these interviews. The students held practical epistemological understandings of scientific knowledge that were described as being developmental, valuable, formulaic, and authoritative. A survey administered at the end of the program was used to reveal students' formal epistemologies of science. These practical and formal epistemologies were described in terms of Sandoval's ("Science Education" 89:634-656, 2005) epistemological themes and then compared for all participants. Findings revealed that, for most students, at least some level of consistency was present between their formal and practical epistemological understandings of each theme. In fact, for only one student with one theme, no consistency was evident. These results hold implications for the teaching, learning, and assessment of NOS understandings in these contexts as well as for the design of apprenticeship learning experiences in science.