I had 2 kids with adhd at boarding schools. The one at Millbrook did get extra time which he used some times but not every time. The one at Hotchkiss did not. Hotchkiss (and I’d guess schools like Hotchkiss) is NOT set up to deal with learning differences. The pace is FAST and that doesn’t, and can’t, change. Miss an assignment or two and things snowball, and the student is quickly underwater. Teachers are used to working with kids who hit the ground running and many do not know how to work with learning differences. I would not send a kid with anything more than very mild adhd to one of the very rejective boarding schools. That is setting them up to struggle/fail.
I would also think long and hard about the need for notes. This is a time for adhd kids to learn the tools needed to succeed in college and the world. After high school no one is giving a kid notes or the equivalent. As much as possible I’d be focused on using the high school years to enable the kid to live without accommodations.
My Millbrook son started out needing tutoring 3x a week in 9th grade, 2x in 10th, once in 11th, and no tutoring in 12th. And then he managed the academics at Emory pretty easily. That’s the kind of path I mean. Hotchkiss would have destroyed this kid.
To be clear, I think both Hotchkiss and Millbrook are phenomenal schools. But neither is phenomenal for every kid. Fit is incredibly important.