For some kids it will also mean more rigor when graduating, as they have an extra year of classes.
S23 has a late birthday and didn’t re-class. Between reclassing and redshirting kindergarten, many of his classmates were 2 years older than him. He started as a soon-to- be 14 year old freshman wearing a kids size 12/14 blazer. Let’s just say he never saw the football field his freshman year. Now he’s in college with lots of kids that also took a gap year so are 2-3 years older.
His boarding school was not highly rejective, but had it been, I’m pretty sure they would have rejected him for 9th and insisted he reclassed if he applied in 10th.