The purpose of this assessment probe is to elicit students’ ideas about density. The probe is designed to find out whether students recognize a change in the mass-volume ratio when the volume changes and the mass stays the same. It is best used with students in grades 6–12, after they have been introduced to the concept of density. 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.