In this paper, I describe the action research I conducted in my third-grade science classrooms over the course of two years. In order to gain an understanding of my third-grade students' ideas about animal adaptations and how the teaching of a unit on crayfish influenced these ideas, I used clinical interviews, observations, and written assessments. I did this research while working as a science resource teacher in a suburban elementary school. The first year, I piloted the unit myself and then made changes to the unit based upon my findings. During the second year, the entire third-grade team taught the unit, and I co-taught with one of these third-grade classroom teachers. I found that students' ideas are developing and that connections to other parts of the science curriculum such as habitats, gases, and plants were necessary yet lacking. Teachers should be prepared to understand these connections themselves and to highlight them to students. Also, as other research indicates, a complex understanding of adaptations is difficult and perhaps not developmentally appropriate for elementary students. Teachers should recognize that elementary students will not develop an understanding of adaptations from merely working with and observing animals in their habitats. Further research is needed to see if the students need specific lessons on adaptations, an understanding of evolution, and/or more experience and maturity in order to truly understand the concept of adaptation.