Large numbers permeate political life; students of political science can expect to encounter a wide range of numbers in newspaper articles, course readings, and statistics. Recent research in cognitive psychology has demonstrated that American adults make systematic errors when comparing numbers in the millions, billions, and trillions. Political decisions made by voters often require weighing large quantities that range across many orders of magnitude, which is difficult without at least a basic understanding of relative magnitudes. If students also lack an understanding of large numbers, professors cannot meaningfully teach students about political phenomena involving such magnitudes. Therefore, we designed and tested an exercise to improve students’ accuracy in dealing with large magnitudes, which had immediate and sustained effects both on their abilities to accurately work with large numbers and their perceptions of numbers in political judgments.