This mixed-methods study was designed to determine the impact of attendance in the professional development series of the school leaders' organization for school leaders and leadership capacity in Tennessee public schools. The areas of focus of the study included leadership practices, instructional practices, and school culture as perceived by teachers and principals. In addition, the relationship between frequency of attendance in professional development sessions and student achievement as measured by universal screener data in reading and math, along with end-of-course data in English and math for high schools was examined. Lastly, the study determined the impact in the 2015-2016 and 2016-2017 school years for principals of Tennessee public schools in the areas of enhanced leadership practices, improved instructional practices, and improved school culture as measured by teachers' responses on the Tennessee Education Survey (TES). Statistically significant differences were found in the student achievement in reading universal screening data, math universal screening data, and English end-of-course assessment data; however, there was no statistically significant difference found in math end-of-course assessment data. There was a statistically significant relationship between attendance in the professional development sessions and reading universal screening data and math universal screening data; however, the relationships between attendance in the professional development sessions and English end-of-course assessment data, along with math end-of-course assessment data was not realized. Finally, there were statistically significant differences found in 2015-2016 and 2016-2017 TES in the areas of teachers' perceptions of the principals' leadership practices, instructional practices, and school culture. [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/en-US/products/dissertations/individuals.shtml.]