This study investigated how teacher mastery goals and self-efficacy mediate the relationship between transformational leadership and teacher outcomes (work engagement, engagement in professional learning, job satisfaction, and intention to quit). A sample of teachers in Singapore (n = 495) completed an online questionnaire. We conducted path analysis to test the hypothesized model based on person measures obtained in Rasch analysis. We found that transformational leadership was associated positively with teacher mastery goals and self-efficacy, both of which partially mediated the relationship between transformational leadership and teacher outcomes. The findings enhance our understanding of the motivational mechanism between transformational leadership and teacher outcomes.