This qualitative case study aimed to investigate instructional leaders' depths of science content knowledge and pedagogical content knowledge and how their depths of that knowledge supports effective instructional leadership. Implementation efforts around the Next Generation Science Standards (NGSS) have highlighted the need for science instructional leaders to have in-depth content and pedagogical knowledge to function as effective instructional leaders in secondary science classrooms across the United States. Semi-structured interviews with 19 teachers and instructional leaders in a public high school in the southern United States informed the study. The findings revealed that teachers expect instructional leaders to have higher levels of science content knowledge and pedagogical content knowledge to serve in their leadership roles. The findings also suggested science instructional leadership is directly related to instructional leaders' self efficacies and self-perceptions. For practical implications, instructional leaders at the secondary level may consider these results for reflection on practice and future planning of professional learning for overall school improvement. Recommendations for future research include expanding the sample population to include multiple school districts, rural school districts, and across content areas. [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.]