In addition to any discoveries that teachers might make about student learning while that learning is in progress, they must still assign grades. Consequently, educators need to develop and implement a system that supports both the formative and summative functions of assessment--formative, in that teachers can use evidence of student achievement to adjust instruction to better meet student learning needs; and summative, in that teachers can amass the information to provide a final grade for a marking period. The first requirement of an assessment system that supports learning is a standards-based record-keeping system. The second is a dynamic grading process in which teachers alter students' grades in light of new evidence of learning. A pilot study conducted in an 8th grade physical science class suggests that implementing such a grading system can improve both student motivation and achievement. (Contains 1 figure.)