In this paper, we report on a program of study called Adventures in Modeling that challenges the traditional scientific method approach in science classrooms using StarLogo modeling software. Drawing upon previous successful efforts with older students, and the related work of other projects working with younger students, we explore: (a) What can younger students learn about complex systems and scientific methodology using this set of educational technology tools; (b) How do they respond to the open-ended nature of the Adventures in Modeling curriculum; and (c) How can the curriculum be adapted to better meet their needs. Using a naturalistic paradigm, we investigate differences between fifth and seventh graders and how, as a group, they respond in a different manner than other older students with whom we have worked. We also evaluate the degree to which their projects and practices embody the modeling and complex systems understanding that we have seen these activities promote in older students. We found that while students initially struggled with several aspects of the complex systems paradigm and required additional scaffolding, most of the students successfully built projects that demonstrated at least a rudimentary understanding of systems and how to analyze them. In comparison, the fifth graders were more readily engaged by the Adventures in Modeling curriculum, perhaps due to the playful design and exploration that StarLogo modeling encourages. This finding echoes other researchers (Rieber, 1996) who have supported a similar notion that student learning at this level could benefit from greater play. This successful implementation of complex systems learning at a young age is important because, like many deep-rooted misconceptions in science, it may be easier to dispel the misconception of the centralized mindset (Resnick, 1994) at an earlier age before it has been reinforced by years of schooling. (Contains 5 figures.)