Components of the School Renaissance[R] program, including Accelerated Reader and Reading Renaissance, have been implemented in more than 65,000 schools in the United States. Despite the program's popularity, there have been no published, well-controlled evaluations of its effectiveness. This randomized field experiment was designed to gauge program impacts on the reading achievement of 978 urban students in Grades 3 to 6. Schools and teachers within schools volunteered to participate in the study, with the foreknowledge that teachers would be randomly assigned to either implement School Renaissance or serve as controls. A 3-level hierarchical linear model was used to estimate the impact of the program on student reading growth trajectories on the STAR Reading test. Students in School Renaissance classrooms exhibited significantly higher growth rates than those in control classrooms, with effect size estimates ranging from +0.07 to +0.34 across grades. Quality of program implementation did not predict student achievement growth but was correlated with a reduction in the negative effect of learning disability status.