Captiva, each service, even the Coast Guard, have JROTC programs. Some 3,500 different units are in high schools across the United States. You might be confusing it with a military academy (one per service).
The program is generally voluntary, although my daughter's school required each student to do a semester in JROTC.
It's a great program. Some 30% to 50% do end up entering the military.
If a participant joins enlisted, they generally get promoted automatically upon graduating basic. Up to E-3, so it puts them 6 months to 12 months ahead of their peers.
And I was in Marine JROTC. It certainly helped me when I went into to ROTC and to get an Army Scholarship.