Scientific argumentation is the process of evidenced-based reasoning: using data and reasoning to arbitrate between competing claims. By monitoring the cycling of water in the terrain simulator and gathering data from the in-game sensors, students build a body of evidence to make and defend scientific claims. This is the crux of Mission HydroSci – teaching students how to link their understandings of core science ideas with scientific practices, allowing them to make well-reasoned claims and defend those claims. This unit also provides a tutorial to the gameplay.