Recent research investigating the quality in education has examined the processes and structures in effective schools, and they have tried to explain the understanding of management in effective schools by focusing on many variables such as climate, educational processes, and student academic success. The place where the student meets quality education is inside the classroom, and how the teacher manages the educational processes, the strategies and approaches used in classroom teaching play a leading role in the student’s receiving qualified education. Studies conducted in recent years have tried to reveal the direct or indirect effects of school leaders on teaching and learning processes. Based on this trend, the aim of this study is to determine the mediating role of instructional climate in the relationship between school leadership and classroom instruction. We used a cross-sectional research design, one of the quantitative research methods. For this purpose, school leadership, instructional climate, and classroom instruction scales were applied to teachers working in secondary schools. The universe of the research consists of public-private secondary schools in the districts of Karaman province and the teachers working there. In this context, 585 teachers working in secondary schools in Karaman province were reached in the 2020-2021 academic year. Approximately, 60% of the teachers participating in the research were female teachers. In the study, the relationships between the variables were examined based on structural equation modeling. We have four hypotheses: (i) School leadership directly affects the instructional climate, (ii) school leadership directly affects classroom instruction, (iii) the instructional climate directly affects classroom instruction and (iv) school leadership indirectly affects classroom instruction. The results reveal that the school principal's school leadership behaviours directly affect the instructional climate and classroom instruction activities. Additionally, the findings showed that school leaders have an indirect effect on classroom instruction through instructional climate. For this reason, researchers are recommended to test different models with different variables that will explain the indirect effect. We conducted a cross-sectional correlation model while testing the research hypotheses. Longitudinal data should be collected to analyze variables in this regard. Second, we tested the hypotheses via a single-level analysis. Further research should be modelled using the two-level analysis method. Finally, the sample for this research consists of teachers. To get rid of social prejudice while presenting the results, data should be collected from school actors such as students, parents, school principals, etc