The purpose of this assessment probe is to elicit students’ ideas about the concept of matter. It is designed to find out how students define matter and whether they recognize that all three states—solids, liquids, and gases—are matter. It is best used with students in grades 3–8, although some high school students may benefit as a way to recognize that gases are matter. The probe is provided in English and Spanish. A materials list, teacher notes, standards, assessment, and references are provided. This book selection also includes the Table of Contents, Preface, Acknowledgments, Dedication, About the Authors, Introduction, and Index.