There are numerous variations surrounding the utilization of instructional coaches in education. This paper quantitatively examined the relationship between principals and outside instructional coaches and how this relationship impacts the principals' perception of the coaches' support on the school improvement within the large urban K-12 New York City public school district. It also illustrated outside instructional coaches' approaches that have positive influence on school leaders' traits and practices, and on school improvement support, thus, building a connection between the coaching of principals with student achievement. Participants of the study were all New York City public school principals. An online questionnaire with 28 items was used to collect data. Survey administration was anonymous. Two statistical data analysis techniques were utilized in the analyses of each research question: Somer's D test for association and binary logistic regression using Statistical Package for Social Sciences (SPSS, Version 22). This study examined the connection between outside instructional coaches and school support that is directly related to overall school performance and suggested that experienced principals tend to develop principal-coach relationships as a venue of increasing school support. Findings showed that male principals had greater odds of developing a trustworthy principal coach relationship. Also, principals who participated in their outside instructional coaches selections and principals with knowledge about their coaches' collaboration with other outside instructional coaches have greater odds to develop trustworthy principal-coach relationships. Results also demonstrated that a strong correlation exists between principal-coach relationships and school improvement support: the coaches' assistance with any school level initiatives and with any external level initiatives, and the coaches being a source of their principals' professional learning. Furthermore, it was identified that the combination of the trustworthy principal-coach relationship and a coaches' longevity (more than two years) at a school positively influences the principals' perception of school support. Moreover, a strong positive correlation was identified between the principal-coach relationship and leadership traits that are based on Sharkey's (2010) study. In exploring an impact of the studied leadership traits on overall school performance based on a 4-point NYC Quality Review rubric, Culture, Finance, Collaboration, and Listening were the most significant ones. The study also determined a significant statistical correlation between coaches' impact on principals' professional goals and leadership practices. The examination of the data pointed at strong correlations between the following coaches' approaches: customizing support to principals' needs, the context, and the specific situation; discussing and applying adult learning concepts; having goals for each principal-coach meeting; scheduling principal-coach meetings every other week; and using research based knowledge and strategies, and school leader's practices. [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.]