Mercer's 47-year career in independent schools began as a classroom teacher in the fourth grade at Gilman School.   A teacher, coach, and adviser, Mercer's classroom experiences include mathematics, anthropology, history, and science.   Mercer served in a variety of administrative positions at Gilman, and for the last 20 years he was Head of School at three different independent schools:  Boys' Latin, Episcopal Collegiate School, and Southampton Academy.