Current teacher evaluation systems (TES) in pre-kindergarten through 12th grade (P-12) American public schools may be impeding the reflection and feedback processes needed for impacting teachers' professional growth and developing trusting, administrator-teacher relationships. The dominant purpose of summative evaluation has been to rate teachers' performance, possibly leading to high-stakes consequences; whereas formative supervision has involved collecting data through informal means such as non-evaluative observations and follow-up administrator-teacher feedback. Formative supervision's purpose has been to provide support and determine resources and professional development for teachers. Despite contrasting purposes, evaluation and supervision have been commonly conflated, further perpetuating the TES's lack of impact on teachers' professional growth and trusting administrator-teacher relationships.To address this problem of practice, a mixed methods action research study was conducted in an Arizona school district to implement a formative supervision intervention involving cycles of frequent informal observations followed by meaningful, administrator-teacher reflective conversations. The researcher partnered with an administrator and four teachers as they explored their construction of meaning about their formative supervision experiences and its effects on teachers' professional growth and trusting administrator-teacher relationships. Guided by the researcher's Formative Supervision Conceptual Framework, the study found that educator participants believe formative supervision supports teachers' professional growth and helps to build trusting administrator-teacher relationships. Unannounced, frequent, and timely informal observations more powerfully impact teachers' professional growth than do infrequent and announced formal observations. Administrator-teacher reflective conversations involving nondirective, collaborative, caring, and honest approaches to feedback as well as focusing on the teacher's perspectives, reflection, and strengths result in trusting relationships. Due to trusting relationships, teachers feel secure in risk-taking, making mistakes, and asking for administrators' feedback and support. The study's findings present notable implications for P-12 school districts' TES and supervision practices as well as for pre-service administrator preparation through university educational leadership programs. [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.]