The achievement gap refers to the observed, persistent disparity of educational measures between the performance of groups of students, especially groups defined by socioeconomic status (SES), race/ethnicity and gender. The achievement gap can be observed on a variety of measures, including standardized test scores, grade point average, dropout rates, and college enrollment and completion rates. While this article focuses on the achievement gap in the United States, the gap in achievement between lower income students and higher income students exists in all nations and it has been studied extensively in the U.S. and other countries, including the U.K. Various other gaps between groups exist around the globe as well.