This dissertation examines the effects of social network sites on youth social and academic development. First, I provide a critical analysis of the extant research literature surrounding social network sites and youth. I merge scholarly thought in the areas of Internet studies, digital divides, social capital theory, psychological well-being, identity development, academic engagement, and educational technology to understand how researchers might examine new social technologies and youth. Second, I examine the question of digital divide, or whether particular teenage populations do not have access to online social networks. Using a nationally representative dataset from the Pew Internet & American Life study, I explore whether there are disparities in teenage access to social network sites. Third, I report a cluster-randomized trial that was designed to explore whether social network sites have a beneficial impact when used in high school classrooms. A total of 50 classrooms, and nearly 1,400 students were randomly assigned to use an experimental social network site. The results highlight the challenges and potential of this technology when applied to school contexts. [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.]