American Institutes for Research (AIR) conducted an evaluation of the effect on struggling readers of implementing the READ 180 reading intervention in five participating schools in Milwaukee Public Schools (MPS) under a Striving Readers grant from the U.S. Department of Education. The evaluation used an experimental design in order to produce a rigorous estimate of the impact of the READ 180 intervention on measures of reading achievement for struggling students. The evaluation also explored implementation fidelity and the contexts and conditions of implementation that may extend or limit the intervention's effects. To measure program impact on students' academic performance in reading, AIR analyzed student achievement data collected from the Northwest Evaluation Association (NWEA) Measures of Academic Progress (MAP) benchmark assessment. AIR also administered a student survey to assess the impact on student engagement and self-efficacy for reading. This report asked the following research questions: (1) Does the READ 180 reading intervention improve students' academic performance in reading?; (2) With what fidelity did the program implement the professional development model and what factors mediated the level of implementation?; and (3) With what fidelity did classroom intervention teachers implement READ 180 and what factors mediated the level of implementation?