This study investigates the effect of materials developed based on conceptual change approach on 9th grade students'achievement in the subject of fractions. With this aim, a worksheet, conceptual change text and a two-stage performance test on the subject of fractions were developed. Quasi-experimental research model was used in the study. Following this model, the fractions were taught with traditional method in the control group and it was taught using worksheets and conceptual change texts in the experimental group. The performance test was applied as pre- and post-tests to total 46 students studying at two different 9th grade classes of a high school in Trabzon during 2008-2009 school year. The results of the study revealed that the instructional materials increased students' success in the experimental group. Therefore, it's recommended to use the materials developed during the course in mathematics classes and to develop similar materials for other subject matters. [Paper presented at the World Conference on Educational Sciences (WCES) 2010.]