A main objective of classroom management (CM) is to raise students' attention to their daily academic work by creating a classroom environment that supports academic and socioemotional learning. While studies have addressed CM effects on classroom-level behaviour or students' academic outcomes, students' attention skills been largely overlooked. This randomized controlled trial evaluates the effectiveness of a teacher-targeted CM intervention on students' selective attention. Twenty-four primary schools were randomized into receiving the Inclusive And Appreciative Classroom Management (IACM) intervention (treatment) or a general information technology (IT) didactics course (control condition). All participating 1st-grade teachers and their students (N = 1,160) were followed for 1 year. Using repeated measurements of the d2 Test of Attention, we find that the IACM intervention improves students' selective attention with 0.26 standard deviations. The effect is robust to the inclusion of student- and classroom-level characteristics. All analyses account for the variation across students, classrooms, and schools.