The aim of this study is to research the effect of the 5E instructional model on primary (sixth grade) student success during the circulatory system unit. This study was conducted with 38 students in two different classes by the same researcher in 2006-2007. One of the classes was assigned as the control group and the other as the experimental group. Appropriate activities using the 5E instructional model were used in the experimental group, while traditional teaching using question and answer methods was applied with the control group. To compare the treatments, the percentage of correct statements and t test results were used. While initial levels of the experimental group and the control group were the same, a significant difference occurred in favor of the experimental group as a result of the application. (Contains 4 tables.)