This study addressed the extent to which coaching, as a specific type of professional development, impacted teacher behavior and instructional quality. Specifically, this study sought to determine the extent to which teachers understood and used Marzano's nine high-yield strategies as a result of their participation in six weeks of on-site professional development and one-on-one coaching sessions with the school's on-site instructional coach. In addition, this study sought to determine the extent to which teachers considered the instructional coach to be influential in their instructional improvement efforts. Mixed-model ANOVAS were run to compare changes in teacher behavior from pretest to posttest. The results indicated that coaching is a viable way of impacting teacher behavior and transforming the quality of classroom instruction. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]