This study examines the impact of structured professional development programs on teachers’ instructional strategies, classroom management, assessment practices, and overall pedagogical effectiveness. Using a mixed-methods approach, data were collected from in-service teachers through surveys, classroom observations, and semi-structured interviews conducted before and after participation in professional development activities. The findings indicate that sustained and well-designed professional development programs significantly improve teachers’ subject knowledge, instructional planning, learner-centered teaching practices, and reflective teaching skills. Moreover, teachers demonstrated increased confidence, improved classroom engagement, and more effective use of assessment and instructional technologies. However, the study also highlights challenges such as limited follow-up support, time constraints, and contextual factors that may influence the transfer of learned skills into classroom practice. The study concludes that continuous, collaborative, and context-specific professional development programs are essential for achieving meaningful and lasting improvements in teaching quality and classroom practices among in-service teachers.