The Big 4 privates in Charlotte used to get players from public school to come in and they would reclassify. A sophomore goes to the private school and repeats his sophomore year and ends playing high school ball for five years starting with his initial freshman year. The Charlotte Big 4 no longer allow that practice but many privates still do. In some states and with some families they will have a student repeat a grade especially 8th grade to basically do the same thing but stay in the public system.
One thing people should also remember is that in Florida an athlete can play until the day he turns 19 years old and 9 months. A few years ago a top player played through the state quarterfinals but could not play after that due to being three months short of his 20th birthday and still a high school senior. Not unusual there.