The purpose of this assessment probe is to elicit students’ ideas about the particle model of matter. The probe is designed to find out if students recognize that there is empty space between the atoms that make up an object and that the atoms are the only matter that makes up the object. This probe is best used with grades 5–12, but can be modified for grade 5 by referring to particles of matter instead of atoms. 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.