In this dissertation study, we investigated the social validity of Tier 1 practices within tiered systems, with specific foci on the Comprehensive, Integrated, Three-Tiered (Ci3T) model of prevention and the high school context. Specifically, we began by outlining the challenges associated with implementing Tier 1 practices, particularly within high schools, and how social validity may be a potential solution to these challenges (Chapter 1). Then, we described a literature review in which we mapped the literature on social validity in high school settings (Chapter 2). Next, we described the method of a descriptive study to examine the relation of school level (i.e., elementary, middle, high school) on educator ratings of social validity of Tier 1 practices within Ci3T schools at the fall and spring timepoints during the first year of implementing a Ci3T model. Additionally, we investigated how educator characteristics (i.e., school level, gender, age, role, years of experience, highest degree earned, and training on classroom management, academic screening, and/or behavior screening) and initial social validity ratings predicted social validity ratings of Tier 1 practices in the spring (Chapter 3). We concluded the dissertation study by describing results of our analyses (Chapter 4) and describing how the results connected to the literature and point to future directions for researchers and practitioners (Chapter 5). [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.]