Wow @Center that adds a whole new wrinkle - I wasn’t aware of kids repeating while at boarding school, but I guess it makes sense.
I agree that these %s are plausible, since they were corroborated by both the AOs and our tour guides (as well as a random sampling of parents). As someone mentioned earlier, some kids are already old for the grade due to repeating a year when they were younger (usually K). So, between the group that repeats 9th for athletic reasons and the group that is a year older due to an earlier repeat, that can be a large %. Because of that, families/kids are opting to repeat 9th because they just don’t want to be that much younger than their classmates. This is not something suggested or recommended by the school, which every AO that we spoke to was careful to point out (“that decision is up to the family”).
Anyway, based on our initial visits, DS will most likely be repeating 9th.