I conducted a single instrumental case study to address the problem of practice in which approximately one-third of students entering the ninth grade for the 2019-2020 school year in the study school district were reading below grade level proficiency. I chose an instrumental case study method because it allows for an in-depth examination of a situation within its real-life context. I opted for this approach because I sought to understand the problem of practice deeply and generate recommendations for practical application. By focusing on a single case, I could thoroughly explore the intricacies of the subject matter, providing valuable insights that can inform practice, policy, and research (Creswell & Poth, 2018). This study was deemed necessary to address the issue of adolescent reading intervention across the district by answering two research questions: (a) How do rapid coaching cycles affect instructional practices for co-taught READ 180 and English I instruction? and (b) How does the co-taught instructional model of READ 180 and English I instruction affect reading performance for high school students reading below grade level proficiency? I analyzed multiple sources of qualitative and quantitative data, including interviews, observations, documents, and student performance data to develop themes and patterns in order to provide solutions to my research questions and address the identified problem of practice. Results indicated that changes to instructional practices based on rapid coaching cycles reflected a comprehensive approach to enhancing instructional practices, fostering student engagement and accountability, and promoting continuous improvement in the teaching and learning environment. The results of this study have practical implications for informing future instructional practices to address below grade level reading proficiency among high school students through targeted, evidence-based reading interventions at the site, district, and state levels. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]