Purpose – Research on school leadership has confirmed that principals influence teacher and student learning by building an “academic-focused ethos”in their schools. In this study, our objective was to examine if and how the learning-centered leadership of principals influenced academic optimism of teachers and the resulting effects on their engagement in professional learning. More specifically, we examined this hypothesized set of leadership effects among teachers and principals in high schools located in Thailand. Design/methodology/approach – The study was conducted with 1,763 teachers and 152 principals from 159 randomly selected, medium size secondary schools located in Thailand. The research employed multilevel structural equation modeling and bootstrapping analyses in order to test and explore these relationships in a mediation model of school leadership effects on teacher professional learning through academic optimism. Findings – Results of this study reinforce prior research which has found that principal leadership can have significant direct and indirect effects on the professional learning of teachers. This finding is important because, as elaborated earlier, scholars believe that teacher professional learning is a key to sustainable improvement in schools. More specifically, our results extend prior research in two ways. First, as the first study to link Learning-Centered Leadership with Academic Optimism, this study extends findings that point to the role of school leadership in sustaining a culture of academic optimism in schools. Second, this study also established Academic Optimism as a mediator through which school leadership supports Teacher Professional Learning. Research limitations/implications – Although our results support a positive conclusion concerning the effects of school leadership and academic optimism on teacher learning, this was a cross-sectional study. Therefore, caution must be exercised before drawing causal attributions. For example, research has also found that teachers who work in schools that evidence features of a professional learning community are more likely to have a greater sense of collective teacher efficacy, a variable that is also associated with Academic Optimism. Therefore, although our study proposed Academic Optimism as the mediator and teacher professional learning as the dependent variable, it is also possible that this relationship could be reversed or reciprocal (i.e. mutually reinforcing). Future research should continue to examine these possibilities using longitudinal and/or experimental research designs that enable clearer delineation of causal relationships. We also suggest the utility of qualitative and mixed methods studies capable of exploring in greater depth the mechanisms through which school leadership contributes to productive teacher learning. Practical implications – There is a need in Thailand, and elsewhere, to redefine the formal roles and professional standards of school leaders to include learning-centered practices. These standards should be embedded into the redesign of pre-service and in-service education programs for teachers and principals. Webelieve that, at present, relatively few school leaders in Thailand genuinely understand the meaningful impact they can have on teacher learning, and by extension, on student learning. Thus, there is a need for systemic change that recasts the nature of leadership expected from principals as well as the level of lifelong learning expected of teachers. Originality/value – The findings from this research contribute to an evolving knowledge base on how school leaders influence teacher learning in different national contexts. The research also extends prior research by exploring the role of academic optimism as a mediator of school leadership effects on teacher learning.