Phillips Exeter Academy is a coeducational independent school for boarding and day students in grades 9 through 12, and offers a postgraduate program. Located in Exeter, New Hampshire, it is one of the oldest secondary schools in the United States. Exeter is based on the Harkness education system, a conference format of student interaction with minimal teacher involvement. It has the largest endowment of any New England boarding school, which as of June 30, 2016, was valued at $1.15 billion.