This paper reports a study on elementary students' ideas regarding changes in mass associated with melting. An open-ended probe was designed and distributed to fifth-grade students (n = 230). In addition, 50 students were asked their reasons behind predictions on mass change. The written responses indicate that, despite conventional teaching, students have difficulty understanding conservation of mass. Although students' predictions were similar, individual reasons for those predictions differed. In some cases, students used similar reasons for different predictions. Finally, the results of the study highlight misconceptions that have not been reported previously.