Response to Intervention (RtI) is a framework for collecting and using data to match students to interventions of varying intensity. This study examines the implementation of RtI in Grade 1-3 reading in 13 states during the 2011-12 school year, focusing on 146 schools that were experienced with RtI. Full implementation of the RtI framework in Grade 1-3 reading was reported by 86 percent of the experienced schools. Fifty-five percent of these schools focused reading intervention services on Grade 1 students reading below grade level, while 45 percent of the schools also provided reading intervention services for Grade 1 students reading at or above grade level. Students who scored just below school-determined benchmarks on fall screening tests, and who were assigned to interventions for struggling readers, had lower spring reading scores in Grade 1 than students just above the threshold for intervention. In Grades 2 and 3, there were no statistically significant impacts of interventions for struggling readers on the spring reading scores of students just below the threshold for intervention. The following are appended: (1) Members of the Technical Working Group; (2) Data Collection; (3) Survey Sample Definition, Coding, and Analysis; (4) Schools' Decision Rules and Data Used for the Impact Analysis; (5) Estimation Methods; (6) Validity of the Regression Discontinuity Design; (7) Sensitivity of the Main Impact Findings; and (8) Exploratory Analyses. [For the executive summary to this report, see ED560821.]