The focus of this study was to explore my leadership practices to improve teachers' acumen and use of research-based Tier 1 strategies to propel student engagement, thereby increasing student achievement. More specifically, the problem addressed was the decline of student performance for students with disabilities in English Language Arts and the organizational change theories and practices used to eliminate this trajectory. Using improvement science, this 12-week study consisted of two iterative and consecutive Plan -Do-Study-Act cycles that focused on professionally developing teachers to incorporate Tier 1 strategies using the Lesson Study, a collaborative and collegial inquiry approach. The data confirmed that effective use of targeted Tier 1 strategies led to an increase in student learning outcomes, improvements in student engagement, and expansion of students' ability to engage in more complex learning tasks. Teachers reported a desire to expand Lesson Study to the entire school as a professional development approach due to the shared learning experiences and collective teacher efficacy that resulted from their collaboration. They also noted the benefits of using improvement science to tackle an adaptive challenge. Additionally, teachers significantly benefited from shared leadership practices such as teacher facilitation that were utilized during the study. As a result, the intentional focus on adaptive leadership practices coupled with adult learning theory positively impacted the teachers and was successful in fostering academic improvement. [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.]