Teacher motivation remained central to understanding teacher effectiveness and educational quality, particularly in developing contexts. Rural secondary schools in Uganda face challenges such as limited resources, difficult working conditions, and inconsistent incentives, all of which affect teacher performance. While intrinsic and extrinsic motivation have traditionally been emphasized, evidence from a mixed-methods study in Kisoro District shows that professional development motivation is the strongest predictor of teacher service delivery. Guided by Herzberg’s Two-Factor Theory and Vroom’s Expectancy Theory, the study finds that teachers engaged in continuous learning demonstrate higher instructional competence, effective classroom management, lesson preparation, assessment quality, and professional commitment. Quantitative analysis reveals a strong positive correlation between professional development motivation and service delivery, while qualitative interviews indicate that teachers view professional development as a pathway to career advancement, confidence, and adaptation to pedagogical demands. The findings underscore the need to strengthen professional development structures in rural districts to enhance teacher performance and improve learning outcomes.