Incorporating computer-simulation modelling into project-based learning may be effective but requires careful planning and implementation. Teachers, especially, need pedagogical content knowledge which refers to knowledge about how students learn from materials infused with technology. This study suggests that students learn best by actively constructing knowledge from a combination of experience, interpretation and structured interactions with peers and teachers when using technology. Simulations do not work on their own, there needs to be some structuring of the students' interactions with the simulation to increase effectiveness. The purpose of this study was to investigate the effectiveness of project-based learning in a technology-rich environment. A science project, Land-use in Watershed, that takes advantage of Internet facilities was developed and integrated with a simulation software package, Structural Thinking and Experiential Learning Laboratory, with Animation, (STELLA) developed to promote deeper understanding of Land-use by students. The Participants in the study were 72 students in a quasi-experimental research design. Statistical analyses showed that students who participated in the manipulation of the experimental model of the watershed experiment and the STELLA simulation performed best on understanding the watershed concept. (Contains 1 table and 1 figure.)