Following up on the effects of learning environments is essential to learning. The aim of this study was to examine students' mental models related to the concepts of expansion and contraction of materials. The population of the case study consisted of 155 students in a city center in Turkey. The data was gathered using open-ended questions that required a description or visualization of expansion and contraction. Data analysis was carried out in two stages. After coding results, the categories scientific, synthetic, and initial were established and applied to the answers. In light of the findings, students generally have initial mental models at low grade levels but synthetic mental models at high grade levels. The discrepancy is not a failure of the students but because processes of expansion and contraction of material cannot be grasped easily. Therefore, visual models and animations of the processes are suggested for future learning applications.