Ample research findings support the effective role that classroom management strategies play in enhancing students' learning. Drawing upon Iranian high school teachers' classroom management strategies, this article is intended to examine the extent to which these teachers follow assertive classroom management strategies and if these strategies affect students' performance. Conducting a survey including 123 female students, it was found out that Iranian teachers apply classroom management strategies of organization, teaching management, teacher-student relationship, and teacher punishment-rewards (consequences) with varying degrees. In the results section, Pearson correlation is applied between students' achievement and each part of teacher management strategies. Finally, a positive relationship between teachers' assertiveness and students' performance was approved. The findings led to implications for in-service training programs for EFL teachers.