Formative assessment is the process of eliciting students' understanding during instruction in order to make sensitive instructional decisions and provide feedback to enhance students' learning. Research indicates that when used properly, formative assessment can lead to significant learning gains and enhance students' self-efficacy. Drawing on previous research and a framework of relational pedagogy, I studied the positional identities claimed, assigned and negotiated by a middle school science teacher and her students during formative assessment interactions. Critical discourse analysis was used to analyze classroom interactions, teacher debriefings and student interviews. Findings from this study indicated that the teacher normatively positioned herself as authority during formative assessment interactions, yet students were not completely powerless. Through assertions of content knowledge and re-directions of topical focus, students positioned themselves actively and had the capacity to influence the direction and focus of formative assessment. Outside of classroom instruction, the teacher simultaneously positioned herself as both hindered by institutional structures yet actively subverted those structures in both covert and overt ways in the service of meaningful science learning. As indicated from interviews and SPAQ questionnaire responses, many students in this classroom positioned themselves positively in relation to science, the teacher and her methods of assessment, while some felt marginalized. This research has implications for the ways in which formative assessment is used to support teaching and learning in science classrooms. Findings from this study indicate that formative assessment is not simply an instrumental act carried out by teachers, but rather is a relational process that necessarily involves students. As a result, formative assessment should balance authoritative and dialogic discourse as a means for supporting and engaging students as they develop rich conceptions of science while connecting those conceptions to their own experiences. [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.]