This book presents findings from the Reading First Impact Study, a congressionally mandated evaluation of the federal government's $1.0 billion-per-year initiative to help all children read at or above grade level by the end of third grade. The No Child Left Behind Act of 2001 (P.L. 107-110) established Reading First (Title I, Part B, Subpart 1) and mandated its evaluation. This evaluation is being conducted by Abt Associates and MDRC with RMC Research, Rosenblum-Brigham Associates, Westat, Computer Technology Services, DataStar, Field Marketing Incorporated, and Westover Consulting under the oversight of the U.S. Department of Education, Institute of Education Sciences (IES). The present book is the first of two; it examines the impact of Reading First funding in 2004-05 and 2005-06 in 17 school districts across 12 states and one state-wide program (18 sites). The book examines program impacts on students' reading comprehension and teachers' use of scientifically based reading instruction.