The article describes an activity for the author's fifth-grade students called "build the strongest mountain." To them, it was not a lesson--it was a challenge. To the author, it was an activity that turned a run-of-the-mill Earth science unit into a terrific opportunity for students to demonstrate their knowledge of erosion and develop cooperative group skills. As a group, the class discussed our experiences in conducting cooperative group work, performing the assigned role given, and documenting all aspects of this assignment. Students then reflected in their science journals about the activity. Typically, students commented that erosion is difficult to stop unless the land is protected against weathering.