Large numbers permeate political life, and 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 demonstrates 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 them about political phenomena involving such magnitudes. The authors designed and tested an exercise to improve students’ accuracy in dealing with large magnitudes, which had immediate and sustained effects on their political judgments about information involving large numbers.