DescriptionSchool-based prevention and promotion interventions (SBPPI) teach students how to recognize and manage emotions, solve problems effectively, establish positive relationships with others, and develop prosocial attitudes. When implemented effectively, SBPPI have been shown to improve desirable outcomes (e.g., commitment to community, standardized achievement test scores, and attendance) and to reduce undesirable outcomes (e.g., suspensions, drug and alcohol use, and aggressive and violent behavior). Unfortunately, our understanding of how to effectively implement and sustain SBPPI outside of well-controlled conditions is lacking. In order to help build a science of implementation and sustainability, this thesis presents a conceptual framework and a measurement tool for effective SBPPI implementation. The framework differentiates among various phases of implementation, ecological levels surrounding implementation in schools, and factors in the system of implementation that facilitate fidelity and sustainability. This framework is measured by the “Schools Implementing Towards Sustainability” (SITS) scale, which is designed to be “user-friendly” in field settings by being viable and scalable. Analyses from a diverse sample of 157 schools implementing Social-Emotional Character Development (SECD), a type of SBPPI, reveal that the SITS has good reliability, good concurrent and construct validity, and promising predictive validity. The findings of the SITS may help advance both the science of school-based interventions and the science of implementation and dissemination as a whole by demonstrating how to bridge the science/“real world” gap.