Response to Intervention (RTI) is a tiered instructional delivery framework developed to meet the needs of all students and has the potential to improve reading achievement, prevent reading problems, and improve identification accuracy for learning disabilities. Tier 1 typically occurs in the context of the general education classroom and is characterized by evidence-based core instruction. Tier 2 support provides an additional instructional opportunity for students who need re-teaching of previously taught concepts, intensified explicit instruction, and added practice opportunities with high quality teacher feedback. Tier 3 is characterized by highly explicit and systematic instruction delivered in small group formats. The purpose of this poster is to evaluate the efficacy of the Enhancing Core Reading Instruction (ECRI) RTI system designed to prevent reading problems. Using regression discontinuity, the authors compare student reading data between students in Tier 1 and those students receiving Tier 1 and Tier 2 support. In each ECRI intervention school, a fall cut score was used to assign each student to Tier 1 or Tier 2 instructional support (or Tier 3, but this is not a focus in this study). Students in Tier 1 received Tier 1 instructional support and students in Tier 2 received Tiers 1 and 2 instructional supports. Research Hypothesis. They hypothesized that Tier 2 support significantly improves reading. Using a regression discontinuity design (RDD) students in Tier 2 should deviate from the regression line predicted by students in Tier 1.