"Citizen science" popularly refers to a participatory approach in which lay persons voluntarily contribute data toward scientific enterprise. Although citizen science may provide unique opportunities for pre-college students to engage in data-intensive science practices, little is known about whether or how citizen science interacts with students' epistemological beliefs. To address this gap in the literature, I combined survey and interview techniques commonly used in citizen science research with video analysis techniques commonly used in science education research for an exploratory-sequential research study with 24 eighth-grade students who participated in the "Ant Picnic" citizen science curriculum during their ecosystems learning. Participants completed the Epistemological Beliefs Scale survey and follow-up interviews prior to the curriculum implementation to elucidate their epistemological beliefs. To explore the moment-by-moment decisions students made about data in the "Ant Picnic" curriculum, I video recorded six focal groups of students. Critical incident and cross-case analyses of video data from the six focal groups revealed students usually shifted between "looking for answers" or "engaging in data-intensive science practices" at four key points in their reasoning processes. These two epistemic orientations were associated with ways students exercised their epistemic agency and autonomy and the specific data strategies they employed. Survey results did not appear to influence students' epistemic orientations, but rather described their experiences with school science. Results hold methodological and theoretical implications for future research into how middle school students use citizen science data. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]