Teacher effectiveness has been shown to have a greater impact on student achievement than any other single factor. School principals must therefore take measures to ensure that schools are staffed with only the most effective teachers. Teacher effectiveness should be assessed yearly and accurately reflected through teacher evaluation measures. There is, however, substantial research that supports that teacher evaluations do not accurately reflect the knowledge and skill of America's classroom teachers. Poorly performing teachers are routinely given acceptable, even positive evaluations. A variety of reasons for the discrepancy exist, including vague and inconsistent understandings of the factors that constitute teacher effectiveness. Since school principals are the individuals responsible for evaluating teachers, it is important to understand their experiences in providing evaluations to teachers, especially since there appears to be a deficiency in research about the lived experiences of school principals in developing a working definition of teacher effectiveness and using the definition as a foundation for annual assessment. In this qualitative grounded theory study, interviews with six middle school principals from the same district in a northern suburb of Atlanta were conducted. Participants representing schools with a variety of demographic compositions were purposefully selected in order to gather rich textual data regarding the lived experiences of school principals in defining and evaluating teacher effectiveness. Results of the study indicated that teacher evaluation instruments failed to measure the skill set principals within the district felt was necessary in order for a teacher to be considered effective, specifically the ability to build personal relationships with students. These finding imply that school systems should take measures to ensure that the summative teacher evaluation processes they employ align with a common understanding of the skills principals feel a teacher must possess in order to be considered effective. [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.]