This study used longitudinal data on 444 teachers and 3,435 students to examine teacher performance in Ghana. The study is divided into two parts. The first part of the study examined factors that mediate the causal effects of a kindergarten teacher training program on classroom quality and student outcomes. Specifically, it examined whether teachers’ knowledge of the learning content, teachers’ implementation quality of behavioral and instructional practices and teachers’ professional well-being were significant mediators of the treatment effect. It utilized a causal mediation approach, which allowed the average causal mediation effects to be parametrically and nonparametrically identified under a set of minimum conditions. The study found that implementation quality was a significant mediator of positive treatment effect on classroom quality across time. This effect persisted even when teacher knowledge and professional well-being were accounted for. The study also found small marginal mediation effects on student outcomes, including a positive mediation effect on literacy and a negative mediation effect on executive functioning in the presence of all mediators. Overall, this study provides empirical evidence to design future interventions that place more emphasis on the influential pathway of implementation quality to yield positive impacts, particularly in early education contexts. The second part of the study examined teacher profiles that provide diagnostic information about teachers’ instructional strengths and weaknesses. It applied stage-wise cluster analysis to reveal different subpopulations of teachers and study how they relate to student outcomes. The study found six profiles of teachers with varying professional well-being and classroom practices, including two that were significantly associated with positive student learning across all four domains of numeracy, literacy, socioemotional development and executive functioning. Overall, the results allow easy identification of growth opportunities for each profile of teachers that helps provide formative feedback and targeted support to facilitate high quality teaching and maximize positive student learning outcomes.