A longstanding aim of education efforts to position students as knowledge constructors so they are engaged in the building and shaping their learning environment. Current education reforms situate student sense making around authentic science inquiries where students are engaged in the practices of science. In the science classroom, this means students are poised to figure things out by asking questions, carrying out investigations, and constructing models so that are positioned to do the intellectual work. However, structuring classroom environments so that students have more authority with respect to their learning is a challenging. Much of this work has centered on how these learning environments are designed, or function theoretically. But less is known about how teachers support students to participate with intellectual authority in real time: What does it look like when a teacher effectively develops students' intellectual authority? In this dissertation, I answer this question by identifying the epistemic messages about learning that one teacher communicates to his students about the kind of ideas that deserve space in the classroom. A theoretical construct, epistemic messages are the implicit messages a teacher sends about the nature of knowledge and learning. How students make sense of what knowledge is valued and supported at school through the interactive and discursive routines that make up the classroom culture determine how they will participate. In this work, I take a situative perspective that views learning as happening in interaction. These interactions happen moment to moment in response to students' ideas. Guided by these assumptions, I suggest that a teacher's epistemic messages drive the patterns in student discourse, and that these patterns in student discourse influence how a teacher responds, as part of a recursive pattern of interaction that is constantly delivered & interactively negotiated. With this dissertation I conduct a longitudinal instrumental case study of an experienced teacher and his students during a multi-week Earth science unit in his eighth-grade classroom. I complete a line by line analysis of whole group discussion and identify four epistemic messages which I call socio-epistemic messages because they communicate normative aspects of students' participation relative to knowledge building. I identify both horizontal messages that emphasize how learners participate collectively in the activity of knowledge building in relation to each other, and vertical messages that position the students in relation to the ideas they are building together. I characterize each message and identify patterns in the way the messages were communicated over the course of the unit. I used rich description to describe the complex ways in which Mr. M enacted the messages, often delivered in combination, to communicate how he wants the students to relate to each other and to the ideas they are constructing together. Through my analysis, I show that the messages were constantly communicated and negotiated, dynamically framing classroom activity in the moment to moment interactions. I demonstrate how they were infused in both the structure of student's activities and the nature of the classroom discussion. I suggest that messages form the "connective tissue" that set up the conditions for students' knowledge building, by conveying socio-epistemic expectations for participation, which adds a complementary and important dimension to disciplinary aims of science instruction, and to the development of students' intellectual authority. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]