Students in grades 3–5 should frequently make conjectures about mathematical relationships, investigate those conjectures, and make mathematical arguments that are based on their work. They need to know that posing conjectures and trying to justify them is an expected part of students' mathematical activity. Justification will have a range of meanings for students in grades 3–5, but as they progress through these grades and have more experiences with making mathematical arguments, they should increasingly base their arguments on an analysis of properties, structures, and relationships.