This study examines the process by which system thinking perceptions develop within the context of a water cycle curriculum. Four junior high school students undergoing an especially designed inquiry-based intervention were closely observed before, during, immediately after, and 6 years after completing a year long systems-based learning program. The employed research tools included observations, semi-structured interviews, and a number of "concept viewing" tools (drawings, concept maps, and repertory grids). Out of the data, four distinct "stories," each presenting a different way of constructing hydro system mental models, are described. The paper's main conclusion is that students develop their systems mental models and remember the learned material based on learning patterns that tend to remain unchanged over time. Consequently, in order to facilitate efficient and lasting construction of students' system models, learning experiences should harness these, and especially the meta-cognitive learning pattern, which holds special significance for constructing systems. (Contains 3 tables and 7 figures.)