This study explores how and under what boundary conditions school leadership influences teachers' instructional practices in Turkey. Using survey data from a sample of 928 teachers in 87 middle and high schools, the present study tested a moderated mediation model of school leadership's effects on teacher instructional practices, with teacher collective efficacy as the mediator and uncertainty avoidance perceptions of teachers as the moderator. We performed a multilevel structural equation modeling with Bayesian estimation to examine the relationships between our constructs. The results showed significant indirect effects of school leadership on teacher instructional practices with the significant mediator role of teacher collective efficacy. However, the distinct contribution of this study lies in exploring the moderator role of uncertainty avoidance on the effect of school leadership on teacher instructional practices through teacher collective efficacy. Our results enhance the field's understanding of how and to what extent cultural aspects of any given society shape the effects of school leadership practices on teaching.