This document sets forth recommendations for the design of a new science assessment. The assessment resulting from this framework will start a new NAEP science trend (i.e., measure of student progress in science) beginning in 2009. This framework represents a unique opportunity to build on previous NAEP science work as well as key developments in science standards, assessments, and research. This document is intended to inform the general public, educators, policymakers, and others about what students are expected to know and be able to do in science as part of The Nation's Report Card, a program of the U.S. Department of Education (ED) that reports on NAEP findings. This 2009 framework presents the content to be assessed as well as the conceptual base for the assessment. The new framework incorporates several key features. Its design is based on widely accepted national science standards and assessments in addition to state curriculum standards. However, it is intended to inform development of an assessment, not to advocate for a particular approach to instruction or to represent the entire range of science content and skills. In view of the need to keep the United States and its youth internationally competitive in science and technology, the framework development process gave special consideration to international assessment frameworks, such as those for Trends in International Mathematics and Science Study (TIMSS) and Programme for International Student Assessment (PISA). The breadth of the science principles represented in the source materials made it necessary to focus on the foundational and pervasive knowledge within each discipline and to pare down the science content to be assessed. The framework is based on scientific knowledge and processes derived from tested explanations and supported by accumulated empirical evidence. Explanations of natural phenomena that rely on nonscientific views are not reflected in the framework. Science content is presented in detailed, grade-specific charts that also allow the reader to see the progression in complexity of ideas across grades. Every attempt has been made to be free of error in describing the science content. The language used strives to be accurate but not technical so as to make the framework accessible to a wide audience. The focus is on students' conceptual understanding, that is, their knowledge and use of science facts, concepts, principles, laws, and theories. Students' abilities to engage in some components of scientific inquiry and technological design are also reflected in the framework. New types of items are recommended, including the use of interactive computer tasks. This document contains four chapters: (1) Overview; (2) Science Content; (3) Science Practices; and (4) Overview of the Assessment Design. Appended are: (A) Steering Committee Guidelines; (B) NAEP Science Preliminary Achievement Level Descriptions; (C) Sample Items and Scoring Guides; and (D) Group 2 Small-Scale Special Studies. (Contains 24 exhibits and a bibliography.