Texas A&M University-Commerce has implemented supplemental instruction (SI) for Calculus since the fall of 2013. A direct display of the ABC rates from fall 2005 to spring 2021 only presents fluctuation from semester to semester, and one can hardly deduce that the ABC rates are increasing. In this paper, the "moving average" technique is used to reveal the effectiveness of SI in improving the percentage of students earning a grade of A, B, or C (ABC rates) in Calculus. Our longitudinal data under the "moving average" also shows that the SI implementation increased the ABC rates of major ethnic groups.