This can't work for every club/program but we has worked for us. We have a dedicated boat j105 that is just for the juniors. They get to sail together and get experience doing all the jobs. (How often do juniors get to helm big boats.) They are getting the skills needed to make them sought after crew when they turn 18 and age out of our junior big boat program. We had about 28 kids in the program with about 15 making up the core group. All races they have an adult abroad for coaching. Sometimes they just take the boat out and go for a sail with no adult aboard.
The past two summers juniors with no adult supervision have taken the boat on the YC annual cruise. This included multiple overnight 100+ mile delivery's at the beginning and end. Anchoring overnight, something most of the adult members of the club don't like to do!! Net net they have gained the confidence and experience to handle the boat in all conditions. They are part of the adult program, although sailing on their own boat. Kind of like the front page picture of the all girl crew a few days ago.