Student problem behaviors in early elementary school are associated with fewer learning opportunities, poor relationships with teachers, and academic and behavioral problems, including increased risk of emotional/behavioral disorders (EBDs). This study examined the effect of BEST in CLASS--Elementary (BEST in CLASS-E), a Tier 2 intervention delivered by teachers, on student problem behavior, academic achievement, teacher-student relationships, and classroom quality using a randomized controlled trial design. Participants were 45 kindergarten to grade 3 students identified at risk of development of EBDs and their 26 teachers from three elementary schools located in an urban school district. BEST in CLASS-E was found to decrease teacher-reported student problem behavior and increase teacher-student closeness; no effects were noted for academic achievement or overall classroom quality. Results suggest the promise of BEST in CLASS-E as a Tier 2 intervention delivered by teachers in elementary classrooms. Implications and limitations of the study are discussed. [This article was published in "Journal of Positive Behavior Interventions" (EJ1265201).]