Which USA high school has won the most national high school basketball championships? I think it is Oak Hill Academy, but would appreciate knowing how many they have won and who are the next best high schools in order. Many thanks.
There is no national championship for high school basketball. These are done at the state level and these are even done by school sizes at the state level.
The tournament you may be referring to is in no way a national championship... It is called High School Nationals because teams on a national level are invited. There is no mechanism to invite the "top 10" teams for the tournament as being a top 10 team in high school basketball would be very arbitrary. They invite who ever they want and most likely the big name high schools - and they invite many of the same teams every year.
Think about this in college basketball they invite ~64 (yes know its more) teams out of about ~350 D1 programs. Most of these programs play each other on a one level off (each team probably plays a team that plays a team in the 350). Even these rankings within this range are highly subjective so they invite 65 teams.
In high school there are over 18k teams. Eight were invited. One of the teams invited was IMG Florida, which is a paid training facility for international students, does not abide by any state high school rules and is not even eligible to win the Florida state championship.
GEICO High School Nationals Tournament (formerly called the National High School Invitational and then the Dick's Sporting Goods High School Nationals) began in 2009.
In the boys tournament, Montverde Academy (FL) has won four times, in 2013, 2014, 2015, and 2018.
Oak Hill Academy (VA) has only won the title once, in 2016.
For the girls, two schools have won the title twice: Riverdale Baptist (MD) in 2012 and 2014, and Miami Country Day (FL) in 2015 and 2017.
Source: GEICO Nationals history
Wyandotte High School in Kansas City Kansas has two. In the early 20th century there actually was a national tournament that was not invitational, i.e. you had to win your respective state and regional tournaments to qualify. I believe the national tournament was played at Madison Square Garden