<Tr> <Td> Master's degree </Td> <Td> 7.62% </Td> </Tr> <Tr> <Td> Doctorate or professional degree </Td> <Td> 2.94% </Td> </Tr> <P> Higher education in the United States is an optional final stage of formal learning following secondary education, often at one of the 4,495 colleges or universities and junior colleges in the country . In 2008, 36% of enrolled students graduated from college in four years . 57% completed their undergraduate requirements in six years, at the same college they first enrolled in . The U.S. ranks 10th among industrial countries for percentage of adults with college degrees . Over the past 40 years the gap in graduation rates for wealthy students and low income students has widened significantly . 77% of the wealthiest quartile of students obtained undergraduate degrees by age 24 in 2013, up from 40% in 1970 . 9% of the least affluent quartile obtained degrees by the same age in 2013, up from 6% in 1970 . </P> <P> Like high school, the four undergraduate grades are commonly called freshman, sophomore, junior, and senior years (alternatively called first year, second year, etc .). Students traditionally apply for admission into colleges . Schools differ in their competitiveness and reputation . Admissions criteria involve the rigor and grades earned in high school courses taken, the students' GPA, class ranking, and standardized test scores (Such as the SAT or the ACT tests). Most colleges also consider more subjective factors such as a commitment to extracurricular activities, a personal essay, and an interview . While colleges will rarely list that they require a certain standardized test score, class ranking, or GPA for admission, each college usually has a rough threshold below which admission is unlikely . </P>

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