I know that colleges tend to do this (readers will cover all applicants from one high school).
Anyone have knowledge about how competitive independent school admissions committees work?
Does one reader get all files from a sending middle school?
Not sure if they use a single reader. But I do think that if there are multiple applicants from the same school, it makes it much more difficult for the applicant. This is particularly true if there are lots of legacy applicants in the pool. In some cases, it can help as they have accepted a large number of kids from that school in the past.
You can really only put in your best application and hope for the best.
At the schools I know the admissions officers cover geographic territories, so yes that AO will read all the applications from the same school. As the other poster said all you can control is your own application. The schools can sometimes be looking for very specific things, like, a 9th grade girl day student. If you are a boy boarder you are out of luck. Or, if you are a girl day student, you are in luck!
All the schools ask for your school, school profiles, and such, so I assume they sometimes do this. It shouldn’t really affect your application much, though.