This study attempted to understand the school principal's perception about the characteristics, attitudes and behaviors of teachers who may be operating on the fringes of proficient performance. In addition, this study attempted to understand if the demographics of the school principal and the school could play a role in the type of characteristics that principals valued. Furthermore, this research also focused on the strategies principals used to address underperformance and barriers that may have faced as they attempted to address instances of teacher underperformance inside the schools they led. This study included a large sample of 410 school principals in the state of Pennsylvania from over 200 school districts. Findings indicate that school principals valued a lack of classroom management, and poor teacher pedagogical skills and subject matter knowledge as strong indicators of underperformance. Principals also identified the use of continued formal documentation and formal improvement plans as strategies to address underperformance. In addition, principals often identified that a lack of time to work with underperforming teachers was a significant barrier as well as protections from teacher unions and a perceived lack of support from the school superintendent and school board. In total, this research has implications for both school district leadership and school leaders. The voice of the principal is an important voice to be heard particularly when it relates to teacher quality and addressing teacher underperformance. [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.]