This longitudinal study examined the role of metaconceptual awareness in the change and the durability of preservice teachers' conceptual understandings over the course of several months. Sixteen preservice early childhood teachers participated in the study. Semi-structured interviews were conducted to reveal the participants' conceptual understandings of lunar phases (pre, post, and delayed-post) and level of metaconceptual awareness (delayed-post only). Based on the change and stability in participants' conceptual understandings from pre to post and from post to delayed-post interviews, participants' conceptual understandings were assigned into three groups that described the profile of their long-term conceptual understandings: "decay or stability", "continuous growth", and "growth and stability". The results indicated that participants in the "continuous growth" and "growth and stability" groups had significantly higher metaconceptual awareness scores than participants in the "decay or stability" group. The results provided evidence that metaconceptual awareness plays a more decisive role in the restructuring of conceptual understandings than the durability of conceptual understandings.