Political division in the United States is the subject of much analysis in the fields of political science and psychology. While political partisanship looms large over discussions of the national political climate's influence on schools and classrooms, very little work exists that directly examines the effects of high school students' political beliefs. Prior research on adults indicates that political partisans are different from their non-partisan counterparts in terms of political knowledge and efficacy. Further, studies often detect biases in adults' processing of political information. Although social studies scholars are beginning to address issues of political division, researchers have yet to directly examine how partisanship influences students' perceptions, behaviors, opinions, and learning. The study described in this dissertation attempts to address this gap. The present research is built around an online discussion of a controversial issue. Using data from three surveys, a discussion forum, and student interviews, I examine differences between partisans and non-partisans prior to the discussion, differences in behaviors these two groups exhibit during a discussion, differences in outcomes following a discussion, and differences in partisan and non-partisans' ability to consider arguments. The findings of this study generally support the argument that, similar to adults, adolescent partisans are substantially different from non-partisans in terms of their political perceptions, behavior, and cognition. There are, however, important contextual factors, such as having an open classroom climate and composition of the discussion groups, which can alter the impacts of students' partisan identities. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]