In this study we described an action research project enacted by a veteran Kindergarten teacher (Sarah) in the context of a professional development program. Over the course of a year, Sarah collaborated with other teachers in a small group to investigate how to use "Science Talks" to promote student learning in Kindergarten classrooms. A Problem-Based Learning approach was adopted to guide the collaborative action research. Based on a rich set of data sources, we concluded that Sarah's action research improved student learning and led to her own professional growth. We also identified important conditions in support of action research.