As part of a project designed to develop, among other tools, an assessment for measuring middle school understanding in plate tectonics, researches from Horizon Research, Inc. (HRI)--a research firm specializing in science and mathematics education--interviewed middle school students about their ideas in plate tectonics and processes that shape the Earth. The purpose of the interviews was to uncover common, incorrect student ideas that could serve as distractors for the multiple-choice test being developed.