In the United States a preparatory school, or prep school, is usually a private secondary school (or high school) designed to prepare a student for higher education. In the United Kingdom and some parts of the Commonwealth of Nations, a Preparatory School, or Prep. School is a private primary (elementary) school, designed to prepare a student for fee paying Public Schools.

Both forms have some things in common. Many are boarding schools; often, such schools are highly selective and academically challenging; they are largely independent of state or local authority control. Such schools are usually expensive, with high tuition used to pay excellent teachers and provide enriched learning environments, through features such as large libraries, advanced science laboratories, and new computers. British and New England preparatory schools, in particular, place a strong emphasis on sports.

In the United States, college preparatory schools often place an emphasis on offering a wide variety of Advanced Placement courses, rigorous academic programs, and small class sizes of 20 or less. Admission is rigorously selective and often based on standardized college entrance exams like the SAT.

The preparation for college that such courses provide, the higher-than-average SAT scores, and other attributes of their students lead many colleges and universities to actively recruit prep school students. In the United States, preparatory education is also often associated with the Preppy subculture.

Because they pay well (and/or offer superior working conditions), American college preparatory schools are often able to recruit faculty and staff with graduate degrees from the top universities, particularly the Ivy League. In contrast, most teachers at public schools usually hold only a bachelor's degree (which may not even be in the field that they teach) and a teaching certificate.

International preparatory schools

Internationally well-regarded preparatory secondary schools include Upper Canada College in Toronto, Ontario, Canada, Appleby College in Oakville, Ontario, Canada, Schule Schloss Salem in Salem, Germany, Institut Alpin Videmanette in Rougemont, Switzerland, and Institute Le Rosey in Rolle, Switzerland.

Partial list of notable U.S. preparatory schools

The following is a partial list of preparatory schools in the United States:

• Brownell-Talbot School (Omaha, Nebraska)
• Choate Rosemary Hall (Wallingford, Connecticut)
• The Collegiate School (New York City, New York)
• The Dalton School (New York City, New York)
• Deerfield Academy (Deerfield, Massachusetts)
• Emma Willard School (Troy, New York)
• Georgetown Visitation Preparatory School (Washington, DC)
• Governor Dummer Academy (Byfield, Massachusetts)
• Groton School (Groton, Massachusetts)
• Harvard-Westlake School (North Hollywood, California)
• The Hill School (Pottstown, Pennsylvania)
• Hopkins School (New Haven, Connecticut)
• Horace Mann School (Riverdale, New York)
• Hotchkiss School (Lakeville, Connecticut)
• Kent School (Kent, Connecticut)
• Lawrence Academy at Groton (Groton, Massachusetts)
• Lawrenceville School (Lawrenceville, New Jersey)
• Loomis Chaffee School (Windsor, Connecticut)
• MICDS (St. Louis, Missouri)
• Middlesex School (Concord, Massachusetts)
• Millbrook School (Millbrook, New York)
• Milton Academy (Milton, Massachusetts)
• Morristown-Beard School (Morristown, New Jersey)
• Noble and Greenough School (Dedham, Massachusetts)
• Northfield Mount Hermon (Northfield, Massachusetts)
• Peddie School (Hightstown, New Jersey)
• The Pembroke Hill School (Kansas City, Missouri)
• The Pingry School (Martinsville, NJ)
• Phillips Academy (Andover, Massachusetts)
• Phillips Exeter Academy (Exeter, New Hampshire)
• St. Andrew's School (Middletown, Delaware)
• St. Mary's Preparatory (Orchard Lake, Michigan)
• St. Paul Academy and Summit School (St. Paul, Minnesota))
• St. Paul's School (Concord, New Hampshire)
• Sidwell Friends School (Washington, DC)
• Strake Jesuit College Preparatory (Houston, Texas)
• Tabor Academy (Marion, Massachusetts)
• The Thacher School (Ojai, California)
• The Walnut Hill School (Natick, Massachusetts)
• Williston Northampton School (Easthampton, Massachusett)
• Worcester Academy (Worcester, Massachusetts)

British Preparatory Schools

• Dragon School, Oxford
• Haslemere Preparatory School, Haslemere
• St Ives School, Haslemere (http://www.st-ives.surrey.sch.uk)

Partial list of Canadian preparatory schools

• St. Michael's College School (Toronto, Ontario)
• Upper Canada College (Toronto, Ontario)
• Trinity College School (Port Hope, Ontario)
• Appleby College (Oakville, Ontario)
• St. George's School (Vancouver, British Columbia)

In France, some high schools offer special postgraduate classes, equivalent in level to the first years of university, for students who wish to enter Grandes Écoles.