Simple harmonic motion (SHM) is an important topic for physics or science students and has wide applications all over the world. Computer simulations are applications of special interest in physics teaching because they support powerful modeling environments involving physics concepts. This article is aimed to compare the effect of computer-assisted teaching (CAT) realized from the simulations of software developed by the researchers for the interactive-physics program and traditional teaching methods on the success of the science prospective teachers and to determine the effect of their concept learning on SHM. The study was conducted in 2008 to 2009 academic year and was carried out in two different classes taught by the same teacher, in which there were seventy freshman science student teachers, attending to Amasya University Science Education Department. An experimental research design including SHM test was applied at the beginning and at the end of the research as pre-test and post-test. After the practice, general achievement in SHM test increased by 15% in favor of experiment group at (p less than 0.05) significant level. Research findings strongly supported that computer simulations might be used as an alternative instructional tool to help students develop their understanding of physics and CAT is more successful than traditional teaching methods. (Contains 2 figures and 8 tables.)