This study aims to examine the effect of instructional materials developed on the basis of 4 stage constructivist model on the success of 6th grade students in the subject of decimal fractions. For this purpose, a worksheet on decimal fractions, a conceptual change text and an anology map were developed. These instructional materials were administered to 62 students selected from two different 6th grade classes in a primary school in Trabzon in 2008-2009 school year. Semi-experimental method was used in this study. At the end of the study, it was seen that the instructional materials developed increased students' success. [Paper presented at the World Conference on Educational Sciences (WCES) 2011.]