Purpose: In 2014, Turkish policymakers implemented a policy change in the school inspection system that encouraged school principals to conduct classroom observations and provide feedback to teachers as a means to improve teaching. However, the question of whether or to what extent such feedback has an impact on teaching has not previously been researched. The study presented in this article scrutinizes the relationship between classroom observation feedback from principals and teachers' classroom practices, as well as the mediating role of teachers' self-efficacy in terms of instructional practices, student engagement and classroom management. Design/methodology/approach: Confirmatory factor analysis and structural equation modeling are employed to examine the relationship among principals' feedback, teacher self-efficacy and teachers' instructional practices using data from the Teaching and Learning International Survey (TALIS), compiled by the OECD in 2018. Findings: These analyses indicate a small but significant direct correlation between principals' feedback and teachers' instructional practices, as well as an indirect relationship mediated by teacher self-efficacy in instructional practices. Research limitations/implications: The findings support the policy shift in Turkey by concluding that classroom observation feedback from principals makes contributions to the improvement of instructional practices. Originality/value: This study establishes a connection between teachers' classroom practices and leadership behaviors, which has not been extensively researched in developing nations.