In the present study, the Incredible Years Teacher Classroom Management (IY TCM) program was implemented as a universal preventive intervention in a regular, lower primary school setting. Outcomes for teacher's behavior management practice, problem behavior in the classroom and the school environment, teacher self- and collective efficacy, and classroom climate were examined. Using a quasi-experimental pre-post comparison group design, teacher-reported outcomes were compared between 163 teachers in 21 schools who participated in the IY TCM program and 139 teachers from 23 schools who did not participate in the program. No significant main effects of the IY TCM program on teacher-reported outcomes were revealed by linear mixed model analyses. The findings suggest that further evaluation is warranted. Future research should explore the impact of training teachers more consistently (e.g., provision of additional individual coaching outside the Teacher Classroom Management [TCM] sessions) and over a longer period than provided in the present study.