It is estimated that K-12 public school districts spend approximately nine percent of their annual operating budgets on professional development to enhance the practice of teachers, yet research has found that this significant resource for training does not always yield sustained changes in instructional practices. This phenomenological qualitative study examined the factors that influence teachers from two to New Hampshire public school districts to achieve a sustained change in their instructional practice. An open-ended teacher survey and semi-structured interviews provided insight into the lived experiences of the 34 participants. The study captured the rich descriptions of times when the teachers were able to achieve a sustained change in their instructional practice and times when they did not. The principals and assistant principals detailed how they influence teachers to make practice change and the resources they use to motivate those changes. The data analysis revealed eight factors that influence teachers to make and sustain instructional practice change. The implications of this study extend to educators, administrators, and policy makers by offering insights on how curriculum implementation can be re-designed to address the identified factors and meet the needs of teachers. [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.]