Often the word assessment conjures up the notion of tests or quizzes that occur at the end of a lesson or a unit. These summative assessments take place when an instructional sequence is completed, providing a summary of what students learned. The summative information reports a student’s status for purposes of grading, evaluation, or certification. Although results may be provided to parents, school districts, and other external agencies, these results typically have minimal bearing on classroom instruction and student learning. In contrast, formative assessment is used to gain information that improves instruction and advances student learning. Just as a doctor diagnoses symptoms before determining how to alleviate them, a teacher must diagnose student ideas before determining how to help students learn scientific ideas (Osborne and Freyberg 1985).