Mindset, educator's effectiveness, leadership, and teacher performance are constructs that interact within the school environment to impact student success and achievement. A culture of mindset impacts teacher and principal effectiveness. These constructs have an interdependent relationship with one another. Building leaders' mindset influences their behavior, effectiveness, and beliefs. Leaders' effectiveness exemplifies their leadership style and dictates their decisions as well as serves as policy drivers. Teachers' mindsets have a profound impact on the learning performance goals and motivation of students. Finally, educators' performance impacts student achievement and success. The purpose of this study was to expand the research regarding mindset and teacher and principal effectiveness. This quantitative, descriptive study surveyed principals and teachers in Indiana K-12 public schools to determine the impact of their mindset on their effectiveness. The Theories of Intelligence Scale was utilized to determine the principals' and teachers' mindset. In addition, demographic questions such as gender, level of education, experience, and position type, were included in the survey. The results indicated there is no significant difference between principals and teachers regarding mindset levels. The results indicated that Mindset was significantly impacted by the years of teaching experience. In addition, significant differences between principals and teachers regarding effectiveness levels were found. Thus, a major conclusion is that the results indicated that Mindset has a significant positive effect on effectiveness. The study provided information that indicated that by implementing a healthy growth mindset in schools, teachers will be more applicable in their roles as leaders and educators, which will then foster a productive mindset among students in the classrooms, resulting in more positive student academic outcomes and a longer achievement trajectory. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]