This study investigated the effect of concept mapping over traditional instruction on students' understanding and retention of heat and temperature concepts. The sample of this study consisted of 5th grade students from two classes of a elementary school (n=75). One intact class was randomly assigned to the comparison group whereas the other one was randomly assigned to the experimental group. During teaching the topic of heat and temperature concepts in earth science curriculum, the experimental group was taught with the concept mapping instruction while the comparison group was taught with the traditional instruction. The results revealed that the students in the experimental group performed better on heat and temperature concepts. However, it has been found that there was no significant difference between experimental and control group on students' retention scores of heat and temperature concept test. (Contains 2 tables.)