In recent years, there has been a feeling that effective teachers can be fostered by grounding professional development in actual classroom practice. This paper reports how a group of teachers adopted a lesson study approach and worked collaboratively so as to improve their class instruction on "wh"-question formation. Teachers' reflections indicate that the collaborative environment throughout the study enabled them to gain insights into how to improve their teaching strategies. Also identified are some of the problems faced by teachers, which may undermine the gains of lesson study.