A three semester, within instructor, interrupted time series analysis of grading practices was conducted in order to observe the effects of the implementation of a plus minus grading system. Over 260 individual instructor's grades were compared before and after implementation of plus minus grading. The results indicate no overall effect of the grading practice on average student grades at the college. Plus minus grading seems to have no impact on grade inflation or grade deflation. (Contains 1 table and 3 figures.)