Purpose: This study focused on the impact of principals' leadership content knowledge, evaluation practices and teachers' professional learning activities on classroom instruction. Design/methodology/approach: Data were collected from 425 teachers who worked in 46 elementary and lower secondary public schools within two provinces in Turkey. Teachers were asked to fill out a questionnaire on principals' leadership content knowledge, evaluation feedback, professional learning activities and changed instructional practices. This study employed multilevel structural equation modeling (MSEM) by using the Bayesian estimation method to analyze the research hypotheses. Findings: Findings indicate that if teachers perceive the evaluation progress as more useful, then they will participate in more professional learning activities, and they will be more effective in their classroom practices. This study also indicates that teachers' professional learning activities stimulate their instructional practices. Research limitations/implications: Although the number of schools and teachers allows using multilevel analysis, it limits the findings generalized beyond the sample. To compensate for this limitation, the author confirmed that the sample was representative of the larger population by examining the size of students and teachers, SES and teachers' job experience. The author also conducted a Bayesian estimator to strengthen the test of significance of effects. Practical implications: This study underlines the critical role of leadership content knowledge in evaluating practices and providing useful feedback perceived by teachers in elementary and secondary schools. Principals should lead to instruction by knowing how to address a lack of teachers' pedagogical content knowledge and classroom practices. The Ministry of Education should support principals in becoming effective instructional leaders to observe teachers and provide them meaningful feedback on teaching. Originality/value: Despite increased interest in this construct, research on principals' and teachers' responses to adapt the recent form of teachers' performance evaluation systems is scant, especially in developing countries' context. Moreover, little is known about the paths through which principals can enhance classroom practices by providing useful feedback. Given these trends in policy and practice context, this study provides empirical evidence that principals can enact the teachers' performance evaluation that affects classroom instruction.