Title I of the federal Elementary and Secondary Education Act, as reauthorized by the No Child Left Behind Act (NCLB), requires states to establish standards, assessments, and accountability systems to ensure that every child achieves proficiency in reading and mathematics by the year 2014. This report describes exploratory analyses of the effects of components of the No Child Left Behind accountability system on the achievement of students in affected Title I schools. The analyses used school-level and student-level assessment data from two states and three school districts, employing a quasi-experimental regression discontinuity method to examine whether schools that fell short of "adequate yearly progress" (AYP) or were identified for improvement under NCLB showed subsequent improvements in student achievement. The purpose of the analysis was to explore the usefulness of the regression discontinuity method for examining the effects of the NCLB accountability system. This analysis was conducted under the National Longitudinal Study of No Child Left Behind (NLS-NCLB), which is examining the implementation of key NCLB provisions at the district and school levels. This report divides into five parts. Following the Introduction in Part 1, Part 2 contains: Using RD to Examine the Effects of Not Making AYP and Identification for Improvement. Part 3 continues with: School-Level RD Analysis in Two States; and Part 4 presents: RD Analysis of Student-Level Achievement Data in Three Large Districts. Part 5 concludes with: Summary and Implications. Appended are: (1) Supplemental Tables for Subgroups of Students, and (2) Selection of Sites Included in This Report. (Contains 23 exhibits.)