We view building a proof of concept simulator and accompanying notebook as an initial step towards a design experiment. In partnership with high school teachers we are examining those design elements relative to web interface, underlying model, scaffolding, and pedagogy that maximize the potential of web-mediated, computer simulation environments to:

• Engender cooperative learning at the 9-12^th grade levels focused on an authentic problem \x96 in this case, how land use alters water quality
• Foster appreciation among "tomorrow's citizens" of how scientific knowledge about rivers and watersheds can guide difficult societal choices about managing the environment.
• Apply modeling and simulation to integrate science content and process skills, (e.g., asking questions, forming hypotheses, gathering evidence, analyzing data) in tandem with authentic problem solving.
• Incorporate modeling and simulation into K-12 professional development, and the pre-service and secondary science curriculum.
• Develop flexible, customizable tools to facilitate authentic, performance-based assessments linked closely with the learning process itself.