This case study presents an exploration of shared epistemic agency in the context of knowledge-building activities of middle school students. Central to this exploration has been understanding what actions that are indicative of shared epistemic agency emerged in a middle school context. In addition, the role of metacognitive self-regulation strategies, personal epistemological beliefs, and learning approaches in students' individual performance was investigated. The study was conducted with 60 sixth graders in three classrooms. Data were collected from multiple sources consisting of records of student participation in classroom and in virtual space, student-created artifacts, non-participant observations, and self-report data obtained from students. Methodologically, a grounded theory approach was used to analyze qualitative data and identify actions indicative of shared epistemic agency. Logistic regression analysis was conducted to understand effects of metacognitive self-regulation strategies, personal epistemological beliefs, and learning approaches on students' individual performance. The findings showed that 13 epistemic actions and 2 regulative actions emerged in students' knowledge-building activities. Significant contribution of personal epistemological beliefs and metacognitive self-regulation strategies to students' individual performance in idea improvement was found. [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.]