The KiVa Anti-Bullying Program (KiVa) seeks to meet the growing need for anti-bullying programming through a school-based, teacher-led intervention for elementary school children. The goals of this study were to examine how intervention dosage impacts outcomes of KiVa and how teacher factors influence dosage. Participants included 74 teachers and 1409 4th- and 5th-grade students in nine elementary schools. Teachers and students completed data collection at the beginning and end of the school year, including measures of bullying and victimization, correlates of victimization (depression, anxiety, peer rejection, withdrawal, and school avoidance), intervention cognitions/emotions (anti-bullying attitudes, and empathy toward victims), bystander behaviors, and teacher factors thought to relate to dosage (self-efficacy for teaching, professional burnout, perceived principal support, expected effectiveness of KiVa, perceived feasibility of KiVa). The dosage of KiVa delivered to classrooms was measured throughout the school year. Results highlight dosage as an important predictor of change in bullying, victimization, correlates of victimization, bystander behavior, and intervention cognitions/emotions. Of the teacher factors, professional burnout uniquely predicted intervention dosage. A comprehensive structural equation model linking professional burnout to dosage and then to child-level outcomes demonstrated good fit. Implications for intervention design and implementation are discussed.