The aim of this study is to determine the effect of activities developed in accordance with PDEODE teaching strategy on students' understanding of the particulate nature of matter. The sample of the study consists of the first grade students who study in the Primary School Teacher Education Program. In order to determine the conceptual change on students a test consisting of 8 questions was applied to the sample. This test was applied as pre-test, post-test and delayed post-test. The difference between the measurements was found statistically significant (p<0.05). This result shows that the treatment promotes the conceptual change and enhances students' conceptual understanding. As a result of a post-hoc test (Tukey HSD test) it was established that there is a statistically significant difference between the means of pre-test and post-test, and pre-test and delayed test (p<0.05), there isn't a significant difference between the means of post-test and delayed test (p>0.05).