This paper explores teachers' experiences of using only Persian language in Iranian schools and its consequences. To do this qualitative method and phenomenological approach was employed. Participants included all teachers of K-12 across Sanandaj and fifteen experienced teachers (8 male and 7 female) were selected via purposive sampling. A semi-structured interview was conducted to gather data. Using the Braun & Clarke (Braun and Clarke in Cooper et al. Camic et al. Long et al. Panter et al. Rindskopf et al. Sher (eds), APA handbook of research methods in psychology, American Psychological Association, Washington DC, 2012) framework, thematic analysis was applied for analyzing the data. Despite teachers emphasizing the significance of the mother tongue in various aspects such as Cultural Identity, Sense of Belonging and Communication Knowledge and Skills, they perceive that the educational system enforces a monolingual policy (Persian) through Educational Centralization, Cultural Assimilation, and A Policy of Denying or Neglecting Linguistic Rights. They also highlighted potential consequences of this policy, including Students' Identity and Cultural Crisis, Intensifying Cultural Duality and Hindered Learning. These findings prompt policymakers to consider language minorities in educational planning.