There is a growing consensus that the character of pedagogy must shift from one of teacher- and textbook-directed instruction to one of student-centered learning. This transition stems from the need to maintain the United States’ competitive edge in the world market and prepare young people for a society that is more socially, economically, and politically complex. Progressive educators advocate for a “learning reform” facilitated by digital media, and the skills and competencies that young people develop through using participatory media in an informal setting. This study examined how the use of new media can support subject-area knowledge building and 21st century skills development in nine classrooms in an independent high school. A constructivist grounded theory approach guided the collection and analysis of empirical data. This process took the form of semi-structured interviews with students and teachers, classroom observations, and an examination of course-related documents. A symbolic interactionist perspective framed the data analysis. The study examined wiki use, blogging, microblogging, and document sharing in six high school subject areas: ninth grade History, Latin II, Advanced Placement Art History, twelfth grade English, Anatomy and Physiology, and Environmental Science. Conceptual categories derived from the findings suggest that the use of specific new media tools support subject-area knowledge building, both explicit and tacit. This occurs by promoting participation among all students, which helps students broaden their perspectives through universal access to their peers’ thinking. Findings also suggest that the integration and use of these specific new media tools support the development of certain 21st century cognitive and interpersonal skills. The findings from this study support two substantive theories: 1) The use of new media support knowledge building and skills development through increased participation, leading to broadening students’ perspectives about subject-area content, and 2) as students engage in knowledge building activities, specific features of new media support the development of specific 21st century skills within the cognitive and interpersonal domains. The results of this study provide educators with a set of guidelines to consider as they integrate new media into subject-area curricula, and offer an agenda for further research on a local and national level.