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