This research will investigate the efficacy of Reading Mastery on first graders' reading achievement, reading disability (RD) identification, and risk of RD. Reading Mastery has been used in schools since the 1970s and the 2008 Signature Edition is still widely used today. Despite the many publications that reference this comprehensive reading intervention, its efficacy has not yet been rigorously tested. This study seeks to fill this gap in research by examining the intervention's efficacy, including whether student response depends on student entry-level reading, oral language skills, and cognitive profiles and teacher experiences with explicit instruction. Secondary aims include an investigation of the role played by effective instructional practices, fidelity, and dosage as well as a complete cost analysis and cost-effectiveness evaluation.