Identifying and supporting students in early elementary grades with low literacy achievement is critical to help them achieve grade-level proficiency and stay on track academically. "Reading Recovery"® is an intervention that provides one-on-one tutoring to students in grade 1 with low literacy achievement. This supplemental program aims to improve student reading and writing skills by providing one-on-one tutoring, tailoring the content of each lesson to each student based on observations and analyses of the student strengths and weaknesses from prior lessons. Trained "Reading Recovery"® teachers deliver tutoring daily in 30-minute one-on-one sessions over the course of 12 to 20 weeks. "Reading Recovery"® teachers incorporate instruction in topics such as phonemic awareness, phonics, vocabulary, fluency, comprehension, writing, oral language, and motivation depending on student needs. The What Works Clearinghouse (WWC) reviews existing research on educational interventions to identify evidence-based programs and practices. This WWC intervention report summarizes the available evidence on the effects of "Reading Recovery"® on student achievement in elementary school. [For the Intervention Brief, see ED629012.]