Dialogic teaching has been demonstrated to be conducive to the development of such important competencies and skills as creativity, communication skills, and critical thinking skills. However, the literature confirms that teacher-student interactions in the classroom are predominantly monologic rather than dialogic across subjects, grades, and countries. This article reports the results of a study that assesses the effectiveness of a Philosophy for Children (P4C) programme in facilitating the development of dialogic and inquiry teaching in teachers in Hong Kong. In the study, training and support were provided for teachers to enable them to teach P4C to their students during Integrated Humanities and English lessons. P4C was found to help increase the teachers' effectiveness in the classroom in terms of their ability to engage in dialogic and inquiry teaching, to develop relevant curricular materials for such teaching, to reflect on their own teaching, to recognise their students' capacity for constructing knowledge through dialogic inquiry, to transfer the teaching strategies learned in P4C to other non-P4C lessons, and to identify and analyse philosophical concepts in the school curriculum. The findings of this study suggest that P4C plays a significant role in promoting the professional development of teachers.