At least in the past, Harvard had a far higher rate of students with learning disabilities than lower tier schools, because having one meant you could get unlimited time on the SAT (giving the time to, on the math part, test every multiple choice solution manually rather than solve once and choose or use other higher level strategies).

Richer families were more likely to have connections with a doctor to give the diagnosis, afford the insurance deductible, or even be in the right circles or to know through word of mouth or paid admissions advisers that it was a thing to try and acquire for the kid.