Classroom teachers serve a critical role in developing environmentally literate citizens. In this study, the authors assessed K-8 preservice teachers' understanding of basic ecological concepts. Participants (N = 56) constructed concept maps describing the inter-relationships among 16 ecological concepts. The authors analyzed the concept maps to determine how participants organized, associated, and described relationships between the concepts. Although there was a lack of consistency in associating pairs of concepts, participants often created 2 clusters of concepts: a food web cluster and an ecosystem cluster. Associated pairs were often used in similar ways to describe the relationship among concepts. Concepts such as biotic factors and abiotic factors were frequently not used. It is important to ensure that preservice teachers have a solid understanding of ecological concepts before they begin teaching. (Contains 4 figures and 5 tables.)