The aim of this study is to investigate effects of the guiding materials developed based on the "fire context" and related to "expansion-contraction" concepts in the conceptual understanding of students. A quasi-experimental method has been used in the study. The sample group of the study consists of 5th grade students selected from elementary school. A total of 56 (experiment group 27, control group 29) students from two classes have participated in the study. A concept test, an interview consisting of semi-structured questions, and a drawing test, have been utilised in the research. While no significant difference (U = 345, p>0.05) has been found between the pre test scores of the control group and experiment group students, a significant difference (U = 238, p<0.05) has been found in favour of the experiment group in the post test. A great majority of the students have explained the "expansion-contraction" concept as "mass change". The findings obtained from student drawings support this as well. For future studies, development of materials which emphasise the distinction of the concepts of flexibility and mass change and the concepts of expansion and contraction can be suggested.