The purpose of this primer is to encourage K-12 educators to use consistent and clear prompts structured around the crosscutting concepts to provide a common scientific language that students and teachers use as they engage in the formative assessment process. "A Framework for K-12 Science Education" ("Framework"), (NRC, 2012) and the "Next Generation Science Standards" ("NGSS") (NGSS Lead States, 2013) present significant innovations for how students engage in science learning and, hence, how instruction should also change. The "Framework"'s innovation of using three dimensions has led to significant changes in how standards and instruction are designed. The three dimensions of science education described in the "Framework" are science and engineering practices, crosscutting concepts, and disciplinary core ideas. Science teaching should engage students in performances of science and engineering at the intersection of these three dimensions. Five chapters focus on: (1) Using Crosscutting Concepts to Engage Students; (2) Student Science Performances (importance of using phenomena to engage students; gather, reason, and communicate science performance sequence; and assessing student performances); (3) Attributes of Formative Assessment (culturally relevant science assessment; students' abilities to reflect on their own learning; and measuring three-dimensional learning); (4) Crosscutting Concepts and Student Science Performances (patterns; causality; and systems); and (5) Developing Three-Dimensional Assessment Items. [This report was prepared by the Council of Chief State School Officers (CCSSO) Science State Collaborative on Assessment and Student Standards (SCASS) Committee on Classroom Assessment.]