In his 2011 book "The highly qualified teacher: What is teacher quality and how do we measure it?" Strong argues that as a profession, education has struggled to measure teacher quality and therefore cannot provide a proven system to consistently develop high-quality teachers. In order to move toward an operational definition of teacher quality, Kennedy, in her 2008 journal article entitled "Contributions of qualitative research to research on teacher qualifications" suggests that the causal mechanisms of the development of teachers who are identified as high-quality teachers must be researched, documented, and then used in teacher preparation and development. Instructional ability is a key component of teacher effectiveness. This case study examines instructional transformations made by four teachers to explore why and how teachers make transformations in their teaching. The overarching conclusion of the study is the importance of student-centeredness as a component of teacher effectiveness. [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.]