Externalizing behavior is a significant concern among teachers. Teachers could benefit from incorporating proactive strategies to prevent problem behaviors and promote academic engagement as students transition into the classroom learning environment. The purpose of this study was to conduct an experimental investigation of the Positive Greetings at the Door (PGD) strategy to improve middle school students' classroom behavior. Teachers were nominated by their principals for participation and then randomly assigned to the PGD or attention control condition. Observational data on academic engaged time and disruptive behavior were collected pre- and post-implementation. Results revealed that the PGD strategy produced significant improvements in academic engaged time and reductions in disruptive behavior. Moreover, results from a social validity questionnaire indicated that teachers found the PGD strategy to be feasible, reasonable, and acceptable. The limitations of this study and implications of these findings for teacher pre- and in-service trainings are discussed.