This case study of classroom practice examined what preservice teachers learned about young children's metacognitive thinking processes and constructivist pedagogy through a classroom project. Thirty preservice teachers engaged in a semester-long metacognitive project in which they conducted four sessions with a group of young children. The project was designed to help preservice teachers to foster young children's metacognitive thinking processes and to become reflective about their roles as constructivist teachers. Their final reflections on the metacognitive project experience were analyzed through the theoretical lens of Kroll and Ammon's dimensions of constructivist teacher education. These preservice teachers demonstrated understanding of the key ideas of metacognition and constructivist teaching, including understanding the role of representation in knowledge construction process, building an autonomous learning community, articulating children's knowledge-building processes, and engaging in the cycle of reflective teaching practices. They understood the importance of children's metacognitive thinking in the construction of knowledge and how to adapt their roles as learning partners.