This article examines the efficacy of a multitiered systemic reading intervention for increasing the intensity and quality of explicit literacy instruction that teachers provide in first-grade classrooms. Schools ("j" = 16) were randomly assigned to the treatment or comparison condition. In both conditions, teachers ("i" = 42) provided 90 min of Tier I reading instruction to first-grade students ("n" = 883). In the treatment condition, Tier I classroom teachers were trained to enhance their core reading instruction by making instruction more explicit and intensive through standardized protocols and ongoing coaching support. At-risk treatment students ("n" = 240) also received an additional 30 min of Tier II supplemental reading intervention that was highly aligned with Tier I instruction. The focus of this study is on the Tier I portion of the multitiered intervention and the impact of the Tier I Enhancing Core Reading Instruction intervention on teacher practices. Results indicate positive effects of the Tier I intervention on the quality of explicit instruction and the frequency and accuracy of group practice opportunities provided to students.