This study tests the effectiveness of Well Managed Schools (WMS), an established classroom management program, for improving student-teacher relationship quality, teacher social skills instruction, and teacher self-efficacy. Participants were 415 Grade 1-5 teachers in 49 schools representing 24 school districts across six states in the United States. Teachers were assigned randomly to either the WMS condition (n = 210) or a usual classroom management practices control condition (n = 205). Data were collected via teacher surveys and classroom observations across five waves over two years. Results from analyses of covariance showed a significantly higher adjusted mean level of observed student-teacher relationship quality for WMS teachers (M = 4.12, SD = 0.04) compared to control teachers (M = 3.98, SD = 0.04) at Wave 2 (p < 0.05). Compared to control teachers (M = 3.91, SD = 0.05), WMS teachers (M = 4.14, SD = 0.05) also had a significantly higher adjusted mean level of perceived classroom management self-efficacy at Wave 3 (p < 0.05). Findings indicate WMS improves selected targeted teacher outcomes, suggesting the program may help schools offer effective Tier 1 supports for teachers and students.