Private high schools are nationally ranked by their overall level of instruction, number of graduates attending Ivy League and other top-tier schools, percent of faculty with advanced degrees and factors such as student satisfaction and innovative study tracks. Each of the schools on this list also graduate an above-average number of National Merit Scholars every year, making them some of the best private schools in the United States.

Trinity School

Trinity School in the heart of New York City's Upper West Side has been in existence for 305 years. The school consistently receives high rankings from The Wall Street Journal and Forbes and is number one on The Best Schools' list of The 50 Best Private Day Schools in the United States. Trinity prepares its students for some of the country's top colleges and universities. The school has a six to one student to teacher ratio, and 82 percent of Trinity's faculty hold advanced degrees.

Roxbury Latin School

Boston's Roxbury Latin is an all-boys school that boasts the top SAT average of any high school in the United States. The school also has the highest matriculation rate to Ivy League schools. In existence since 1645, Roxbury is one of the oldest, continuously operating private schools in the country. In 2013, 33 out of 51 graduating seniors earned National Merit Scholarships to some of the country's top higher learning institutions. Roxbury is ranked number two on The Best Schools' list.

College Preparatory School

One of the most highly selective private schools in the United States, College Preparatory School in Oakland, Calif., has an intensive admissions process that ensures only the best students are accepted. In 2013, 59 percent of the coeducational school's graduating class were considered for National Merit Scholarships. Of the school's 55 instructors, 46 hold advanced degrees, including 18 doctorate degrees. Ranked number 17 by Forbes, the school is unique for the number of nationally ranked chess players it has turned out. It also features a week-long "intraterm" during which students are encouraged to intern or travel.

Germantown Friends School

Germantown Friends School is a top coed school located in Philadelphia's Germantown neighborhood. One of the most demanding academic schools in the country, Germantown grads go on to attend some of the nation's top colleges. Two out of 10 students on average attend the University of Pennsylvania. The school is ranked number 14 on The Best Schools list. The school maintains deep Quaker roots and is closely associate with the Society of Friends, which provides the school with its name.