The National Science Foundation-funded research projects described here show the strong link between assessment and improved student learning; the essays invite science teachers to reflect on their practices and priorities and to consider a variety of productive assessment strategies and frameworks. The central ideas around which the chapters are based and which provide compelling data to fuel conversations about assessment purposes and opportunities include the: Roles of assessment in teaching and learning Characteristics of meaningful assessment items Need for research to validate assessment practices Significance of assessing both student knowledge and their misconceptions Value of assessing students ability to apply their knowledge Importance of assessment-focused professional development In addressing assessment as a central element of teaching practice, Assessing Science Learning explores the various forms assessment can take, including student journal entries, feedback on lab reports, observations of students engaged in activities, whole-class discussion, and large annual tests.