In the United States, there are about 26,407 public secondary schools (for 9th or 10th through 12th grade, typically ages 14 to 18). Tuition is free, paid for by property taxes.
There are 10,693 private secondary schools, usually local (the students live at home), run by religious organizations. Tuition is usually around $5000 per year.
And there are about 300 private boarding schools, where the students live full time. Tuition, room, and board are pricy, running $40,000 per year or more, so these schools draw the children of the rich and powerful.

Seriously, nearly everyone I have ever met who went to a boarding school was crazy as a loon.
Here are the most exclusive athletes at the most exclusive boarding schools in the U.S. (many athletes are under 18, so adults will have to wait a few years to ask them out).

1. Choate Rosemary Hall in Wallingford, Connecticut, known as the alma mater of President John F. Kennedy and gay playwright Edward Albee, and for the snub on Family Guy to the effect that Choate guys are up for anything.
These are two cross-country athletes, one with biceps.
2. Church Farm School in Exton, Pennsylvania. Sounds like three random words put together, but it's actually an Episcopal school founded in 1918. Boys only, 190 students.
I couldn't find any athletes, so here are some singers.
3. Deerfield Academy in Deerfield, Massachusetts, one of the oldest boarding schools in the U.S., founded in 1797. One of its traditions is Choate Day, where Deerfield athletes compete against whoever Choate sends over.
4. Groton School in Groton, Massachusetts, another Episcopal school. It's the alma mater of generations of Roosevelts, including the songs, grandsons, and great-grandsons of Franklin and Theodore.
Students apparently play shirtless on the grass.

5. I'm thinking that the Wolfpack is not the best name for the athletic teams at the Hyde School in Bath, Maine. But this wrestler has a nice physique.
More after the break
6. The Kent School in Kent, Connecticut , Episcopal, 570 students. It's the alma mater of Treat Williams, Prince Carl Philip of Sweden, former secretary of state Cyrus Vance, and my friend Zack.
Three swimmers, all in different suits.
7. Phillips Exeter Academy in Exeter, New Hampshire, founded by wealthy merchant John Phillips. Not to be confused with Phillips Andover, founded by his nephew. Both are feeder schools for Harvard.
An Exeter wrestler.
8. St. Andrew's School in Middletown, Delaware, another Episcopal school, where the Orange Goblin's son is attending. But don't hold that against him; he can't help it.
This is the water polo team. They wouldn't do anything as jejune as swimming and diving.
9. Tabor Academy, in Marian, Massachusetts, is known for its marine science courses, a rarity at boarding schools where one is more likely to learn about how to win an election by pretending to be working-class. It offers lots of aquatic athletics, including rowing, sailing, and swimming.
10. Williston Northampton School in Easthampton, Massachusetts (I guess the name Easthampton School was taken).
It has a golf team.