Teaching effectiveness is increasingly highlighted as an important quality in teachers, and teacher education programs have used various approaches to improve preservice teachers' teaching effectiveness. However, how preservice teachers develop their beliefs about effective science teaching and how they enact them in their field experiences have rarely been explored. To better support preservice teachers' professional growth, we investigated their beliefs about effective science teaching, by examining their discourses during collaborative oral reflection sessions in their early field experiences. We also highlighted the possibility of collaborative oral reflection as a medium for improving reflective experiences by evaluating the quality of the preservice teachers' reflections. Theoretical and practical suggestions for science teacher education and future studies are provided.