The quality of a school's social environment is critically related to student outcomes, including academic performance, attendance, student behavior, and high school completion rates. New Hampshire engaged in a dropout prevention initiative between 2006 and 2012 that focused on implementation of the multi-tiered Positive Behavioral Interventions and Supports (PBIS) framework combined with an intensive, student-driven school-to-adult life transition intervention for the highest-need youth. This paper presents a case study of how one high school in the New Hampshire dropout prevention project implemented PBIS at all three tiers of support: schoolwide, targeted, and intensive. The case study includes a description of practices implemented by the school, school and student level outcomes pre-and post-implementation, and successes and challenges experienced by the school staff. The discussion ends with recommendations for practice and research of PBIS implementation in high schools. 2 PBIS IN HIGH SCHOOLS Positive Behavioral Interventions and Supports in High Schools: A Case Study from New Hampshire There is a critical link between social and emotional health and a child's readiness and ability to learn (Zins, Weissberg, Wang, & Walberg, 2004). While school reform has been a national priority for nearly three decades, concerns remain among policy makers and educators that our education system is not adequately meeting the social, emotional, and academic needs of all students (