Reading Apprenticeship is a model of academic literacy instruction designed by the Strategic Literacy Initiative (SLI) at WestEd to improve student literacy skills and academic achievement. Based on understandings of the close relationship between curricular reform and professional development, Reading Apprenticeship includes an instructional framework and associated professional development model for secondary and post-secondary teachers across the academic subject areas. Teachers across the subject areas learn how to build student capacities to carry out intellectually engaged reading, make meaning, acquire academic and disciplinary language, read independently, and set personal goals for literacy development. In 2015, the U.S. Department of Education awarded SLI a three-year Supporting Effective Educator Development (SEED) grant to disseminate Reading Apprenticeship professional learning through the Reading Apprenticeship Across the Disciplines (RAAD) project, a cross-disciplinary blended model of Reading Apprenticeship. Through RAAD, WestEd served 2,240 teachers from 570 schools in 6 states (California, Illinois, Michigan, New York, Texas, and Wisconsin). As part of the grant, IMPAQ International conducted an independent evaluation of RAAD effectiveness. This report presents findings from the randomized controlled trial conducted in California, New York, Texas, and Wisconsin. The impact evaluation employed a group-randomized controlled trial (RCT) in which 40 middle schools from 6 blocks, labeled A through F, were randomly assigned to a treatment group (19 schools), which received the RAAD intervention; or a control group (21 schools), which was set to receive delayed professional development. Grade 7 or 8 English Language Arts (ELA), science, and social studies teachers recruited from treatment schools received the RAAD professional development and ongoing support during the 2016-18 study period, while control schools conducted business as usual. Two years of data were collected from the study schools. Findings from this study demonstrate the success of the RAAD project in offering teachers professional learning and support to scale to help them change their instructional practices to foster metacognitive inquiry, increase class time spent reading, and encourage use of collaboration and reading strategies by students. These findings were accompanied by significant reduction in traditional teacher practices and are consistent with positive findings from other studies of Reading Apprenticeship. However, this study also shows that this iteration of the Reading Apprenticeship fell short of improving student literacy and achievement as measured by standardized assessments.