The most innovative and progressive ideas have arguably come from the minds of American scholars who thrive on the creation of new ways to increase effective instruction and promote life-long learning that is not only essential, but also competitive and exemplary in our global society. And, yet, for decades the American high school has been defined in large part by teacher directed classrooms where students are tracked and required to simply memorize and retrieve information only to remember it for a short period of time to meet minimal criteria for a basic assessment. Such classroom settings can be isolating for teachers and restrictive to those students whose learning relies on instruction that is collaborative, cooperative and personalized. Providing this type of instruction requires increasing the professional knowledge of teachers. Research has shown that teachers thrive in a "teamed" setting and gain extensive content and pedagogical knowledge when working collaboratively with trusted colleagues and where importance is given to time for teachers to meet together to develop, plan and implement curriculum that meets the needs of all learners. The primary purpose of this qualitative study is to examine the role team or co-teaching plays in engaging students in the high school classroom. Specifically, the study aims to understand how teacher practices in a co-taught high school classroom shape the behavioral, cognitive, and affective engagement of students and what factors mediate the co-teaching relationship. Various forms of data will be collected from the classrooms of two co-teaching paired teams working in two different high schools in suburban Massachusetts, including data from classroom observations, teacher interviews, and instructional artifacts. The study is guided by the assumptions that common beliefs about the relationship between instructional practice and student engagement, a desire to collaborate, and administrative support for the co-teaching model are essential to a successful team relationship and positive impact on students' academic and social experiences in the classroom. [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.]