With teacher attrition on the rise and an educational landscape filled with mounting instructional demands and postpandemic challenges, the need for informal teacher leaders has never been greater. Informal teacher leaders, while still in the classroom themselves, are in a unique position to model, coach, collaborate, and advocate for colleagues. They also have the potential to impact pedagogy and school culture due to their proximity and relationships with peers and students. However, there is little research examining both informal teacher leadership and school culture, especially from the perspective of an informal teacher leader. This study was an examination of four dimensions of school culture--professional orientation, organizational structure, quality of the learning environment, and student-centered focus--and how they foster and inhibit informal teacher leaders. The case study also addressed how informal teacher leaders perceive they influence the cultural dimensions. Ten informal teacher leaders participated in interviews. The findings indicated that if trust exists between the adults on campus, then informal teacher leaders perceive they can impact school culture, especially the professional orientation of the staff and the school's student-centered focus. However, organizational structures and the existing professional orientation at a school site could either curb or enhance the informal teacher leaders' leadership capabilities, indicating that a school's culture and informal teacher leaders are intertwined. Recognizing this mutual relationship is paramount to creating environments in which informal teacher leadership can thrive. [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.]