After doing an initial search via the Boarding School Review website that ChoatieMom mentioned, it is useful to have a look at the school's profile. The
School Profile is a ~4 page long document that is available to universities so that universities can acquaint themselves with the school.
The School Profiles summarizes:
- Student Body demographics
- Curriculum offerings
- Athletic/EC offerings
- Diploma Requirements
- Grading System
- Academic Standing criteria
- Course Levels
- SAT / AP scores
- College Matriculation stats
Every school has this document. Here is an example:
http://www.exeter.edu/documents/2012...College(1).pdf
You can Google the document for different schools, but it may take some digging around as the schools intend these documents to be used by universities rather than by student applicants. I find the School Profile to be a useful supplement to the info available on the school websites.