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The current research aimed at attempting to familiarize Greek prospective Pri- mary School teachers with notions of the dynamic systems nature of ecosystem food-webs and evaluate the results. The sample consisted of 85 undergraduate s- tudents of the Faculty of Primary Education, of the University of Athens, Greece, who had chosen the optional topic of the autumn semester: "Environmental Science: The Laboratory Approach". Students were initially given specically designed pre-test worksheets, to nd out their initial knowledge and pre-instructional ideas about the structure and the properties of food-webs as systems. Following this, instructional-teaching took place in four stages. In the first stage of the instruction process, students received real data concerning pellets of barn owls (tyto alba) gathered from two areas of the United States, and were asked to complete given worksheets. At this stage, students' discussions were recorded, hence trying to extract answers to issues such as: the food-webs' ability to reflect biodiversity; their mental representation of a food-web as a system; and what would happen should a "node" of the food-web-network disappear. The second stage involved students interacting with computer software in two phases. In the first, students were asked to reconstruct, on a computer screen, the barn owl food-web, given the arrows and the food-web elements. In the sec- ond stage, students used the System Dynamics Modeler of the NetLogo (version 4.0.4) simulation environment, as an interactive tool for learning. In the third stage, after familiarizing themselves with the Modeler, using the simple predator-prey ecosystem "Wolf Sheep Predation (docked)" model, students interacted with a variation of the Modeler, created in order to learn things about the stability and instability of food-webs as systems and, as a result, of ecosystems. In the fourth-final-stage, following the instruction, post-test worksheets were handed out to students and stratified samples of them were interviewed on fur- ther ideas, predictions and possible extensions of their knowledge.