Giant exploding volcanoes...asteroids crashing into Earth...continents floating across the oceans...massive pools of lava...violent earthquakes splitting continents--middle school students hold a variety of ideas about Earth, how it has changed over time, and what has caused these changes. Listening to students talk about how the world works is fascinating. Some students describe ideas that are essentially correct; others reflect familiarity with the content, but their understanding is incomplete or includes inaccuracies. Still others have little understanding of the content, but imagine dramatic scenes of destruction when questioned about earthquakes, volcanoes, and plate tectonics. Beyond just listening, uncovering students' initial ideas and attending to how those ideas change over a unit of instruction are important to ensuring that students learn scientifically correct ideas. In this article, middle school students were interviewed about their ideas in plate tectonics and processes that shape Earth. This article also discusses the results of the interviews and their implications for classroom practice. (Contains 3 figures.)