This study has three aims; (1) to determine primary school 4(th) grade students' alternative concepts about light, light source and seeing concepts in science and technology program, (2) to prepare a computer supported istructional material (CSIM) for these concepts and (3) to determine the effectiveness of this material in removing misconceptions. To determine students' pre-knowledge, a questionnaire which includes two open-ended questions and a grid applied to students. It was determined that students have the same alternative conception as in the literature. An alternative computer supported material to traditional instructional material was developed and applied for the purpose of removing the alternative concepts and to introduce light sources. After the application of computer supported material, the questionnaire was again applied to the same sample. Data provided from pre-test and post-test are compared and effectiveness of computer supported material in removing the misconceptions were discussed in the paper.