This volcano simulator is unique because it gives a lot of background knowledge for the student to read. As a primary teacher, I would teach this simulator to the class first. You don't always get a major eruption, so they will need to see what the viscocity and gas pressures should be. Documentation of what the pressures are set to and what kind of eruption occured would be important as they figure out this game. Lots of great reading found about volcanos. Good for grades 2-5.
Forces of Nature
Another great simulator for students is the Forces of Nature as they can control what types of forces that they would like to learn more about and then create on their own. Reading and fact finding would be an expectation here. They could define their force of nature before they created one. This simulator is great for grades 1-5.
Simulations for Earth Changes
This erosion simulators has a starting place and then a finishing place. First you choose to use wind, water, volcanos or glaciers to cause the erosion. Then you choose the amount of years and see how the erosion occurs over time. The simulator gives you a goal picture and it's surprising on actual time it takes for erosion to occur. This game gives you chances to pick again. An accountability piece for this simulator would be to chart down their most surprising find and draw it. Great for grades 1-2.