The mobilization of teacher leadership, simultaneous decentralization of power, and centralization of support for teacher-led initiatives is seen as important to educational improvement in post-Soviet Kazakhstan where hierarchical cultures and structures still prevail. The current study reports on results from the Teacher Leadership in Kazakhstan (TLK) initiative, which was based on the internationally recognized Teacher-led development work strategy that enabled teachers to lead individual development projects throughout one academic school year. The TLK initiative involved 16 principals, 32 school-based facilitators, and 150 teachers. Using a mixed-methods design, research for the initiative was conducted over one academic year and collected a wide range of data through questionnaire surveys, interviews, and focus groups. Analysis using structural equation modeling suggested that improved teacher program experience resulted in enhanced teacher leadership capacity, and that teachers from more collaborative school cultures enjoy more impactful initiatives. Semi-structured interviews and focus groups provide further insights into these findings. Implications for policy and practice and future directions are also discussed.