The objective of this research is to investigate students' mental models of the hailstone formation and explore factors that may affect their mental models. The sample chosen for the study was composed of a total of 84 students. The students attended the 1st to 4 th grade classes of the Social Studies Teaching Programme at Giresun University in Turkey. The data in relation to the students' mental models of hailstone formation were collected from the administration of a structured interview consisting of open-ended questions. The students' responses were scrutinised and categorised to gather similar mental models into a group. The choice of categories was based on the students' responses. Four groups mental models have been determined, one is scientifically acceptable and the others scientifically unacceptable. The prevalence of scientifically unacceptable mental models was attributed to the students' lack of pre-knowledge of hailstone formation. Considering the results of the study, recommendations for the teaching of hailstone formation have been made to teachers, textbook authors and programme developers. (Contains 4 tables.)