Supervision based on collaboration, participative decision making, and reflective practice is the hallmark of a viable school improvement program that is designed to promote teaching and learning. Action research has gradually emerged as an important form of instructional supervision to engage teachers in reflective practice about their teaching and to examine factors that aim to promote student achievement. This article examines supervision as it has evolved and moved toward action research advocacy and presents two case studies that show how action research improves teaching and learning. Practical guidelines for implementing action research as instructional improvement are provided for principals.