American university system, like the primary & secondary education system, is largely decentralized, in large part because the Tenth Amendment to the United States Constitution reserves all powers not granted to the federal government or explicitly denied to the U.S. states "for the States respectively, or to the people. Such a degree of autonomy in higher education is rare.American universities have developed independent accreditation organizations to vouch for the quality of the degrees they offer. The accreditation agencies rate universities and colleges on criteria such as academic quality, the quality of their libraries, the publishing records of their faculty, and the degrees which their faculty hold. Nonaccredited institutions are perceived as lacking in quality and rigor, and may be termed diploma mills.
Colleges and universities in the U.S. vary in terms of goals: some may emphasize a vocational, business, engineering, or technical curriculum while others may emphasize a liberal arts curriculum. Many combine some or all of the above.
Two-year colleges (often but not always community colleges) usually offer the associate's degree such as an Associate of Arts (A.A.). Community colleges are often open admissions, with low tuition. Four-year colleges (which usually have a larger number of students and offer a greater range of studies than two-year colleges) offer the bachelor's degree, such as the Bachelor of Arts (B.A.) or Bachelor of Science (B.S.). These are usually primarily undergraduate institutions, although some might have limited programs at the graduate level. Many students earn an associate's degree at a two-year institution before transferring to a four-year institution for another two years to earn a bachelor's degree.
Four year institutions in the U.S. which emphasize the liberal arts are liberal arts colleges. These colleges traditionally emphasize interactive instruction (although research is still a component of these institutions). They are known for being residential and for having smaller enrollment, class size, and teacher-student ratios than universities. These colleges also encourage a high level of teacher-student interaction at the center of which are classes taught by full-time faculty rather than graduate student teaching assistants (TAs), who do teach classes at Research I and other universities. Most are private, although there are public liberal arts colleges. In addition, some offer experimental curricula, such as Hampshire College, Beloit College, Pitzer College, Sarah Lawrence College, Grinnell College, Bennington College, New College of Florida, and Reed College.