A vast amount of contemporary research has been devoted to defining effective school leadership roles and practices and measuring their influence on school processes, structures and outcomes. This paper examines the effects of trust in principals and school leaders' focus on instruction on teacher collaboration and teacher self-efficacy. Using teacher survey data collected from 45 lower secondary Turkish schools across the country in the 2018-2019 academic year, this study employs multilevel structural equation modelling with Bayesian estimation to investigate the structural relationships between trust in principals, alongside leaders' focus on instruction, and teacher collaboration and teacher self-efficacy. The study confirms previous research, indicating that trust in principals has a crucial role in teachers' emphasis on instruction and that these principals' instructional leadership practices enhance teachers' sense of efficacy both directly and indirectly through teacher collaboration. The research concludes that, while the way these practices are carried out might differ across contexts, the principals' leadership practices focusing on teaching and learning still matter for teachers' beliefs and practices in non-western countries. Implications for policy, practice and further research are discussed.