This paper examines the effects of instructional leadership on the change in teachers' classroom practices, with the mediating role of shared practice and learning effectiveness. The study employed a cross-sectional survey design, using quantitative methods. Confirmatory factor analysis and structural equation modeling were used to analyze the data collected from 350 teachers in primary and secondary schools in various provinces of Turkey. The results provided evidence consistent with the previous research from western English-speaking societies, suggesting an indirect relationship between leadership and teachers' instructional practices with the full mediation roles of shared practices among teachers and their sense of agency in learning effectiveness. This work concludes that teacher learning and collaborative practices among teachers, influenced by principals' instructional practices, can facilitate a significant change in several diverse components of classroom instruction, such as the quality of grouping, questions, homework, instructional strategies and differentiated practices.