Grades matter. College grading systems, however, are often ad hoc and prone to mistakes. This essay focuses on one factor that contributes to high-quality grading systems: grading accuracy (or "efficiency"). I proceed in several steps. First, I discuss the elements of "efficient" (i.e., accurate) grading. Next, I present analytical results indicating how often our grading schemes are likely to be inefficient, and I also discuss the causes for grading inefficiency. The following sections describe ways to make our grading systems more efficient, especially by increasing the number of scores and by providing clearer guidance on what constitutes high-quality performance. Finally, I offer data from my own "natural" experiment in grading and offer some concluding comments. (Contains 3 figures and 25 notes.)