This may help : http://talk.collegeconfidential.com/prep-school-admissions/1545276-2013-14-hidden-gem-applicant-thread-p4.html I’ve brought you to page four because there are blurbs and links to school websites but the entire thread is worth reading.
Also- If Thacher is on your WC list, I would suggest adding a school like Berkshire http://www.berkshireschool.org/ to your EC list.