New York Times had an interesting podcast recently where they talked about how so many children are being diagnosed with autism to the point where it's hurting the severely autistic student population (https://www.nytimes.com/2025/11/24/podcasts/the-daily/autism...). There's a finite set of resources pooled for special needs students, and now most of these students have relatively minor symptoms compared to those with "profound autism" (which is a severe disability associated with the inability to speak or live independently).
I suspect this is similar - rich parents are doing anything for an edge in their child's education and can get any diagnosis they desire. It's an unfair system.
They go to other rooms. I had several friends who would not be around during the exam days. On a high stress day like final exam day it's hard to notice but they were definitely gone (so like 1-2 people in a 20ish person class). UC system, mid 2010s.