Thetford Academy opened in February, 1819, and was chartered by the State of Vermont as an Academy on October 29, 1819. There is no statement of purpose in the charter beyond its being termed "an academy." The constitution of Vermont called for free elementary schools in each town, a school in each county for studies above the elementary level, and one university for the state. The terms Grammar School and Academy were used interchangeably to describe the second level of a three-level system. Their purposes were initially to prepare students in classical languages, mathematics, "natural philosophy," and the arts for entrance into colleges and universities, which in turn prepared their students for the ministry, law, medicine, and teaching. By the time Thetford Academy was founded, girls were being admitted to some academies (usually in the summer term) for studies which were advanced beyond the common schools but which were not intended to prepare for college. Thetford Academy was open to both boys and girls from its founding.
An 1864 catalog describes the school as follows: "Thetford Academy is situated in the pleasant and quiet village of Thetford, Vt., two miles from the Connecticut and Passumpsic Railroad. The location is remarkably healthy, and free from business, excitement, and every temptation to lateness and dissipation. The society is characterized by intelligence and morality, and a deep interest is felt in the welfare of the students and the prosperity of the school. "The School is divided into two departments, English and Classical. Instruction is given in the Elementary and Higher English Branches, Latin, Greek, French, Drawing, Painting, and Music. Students are fitted for College, for professional teachers, or for business. The regulations require the students to regard all the proprieties of a sober, industrious and enlightened religious community. The teachers aim not to teach a sectarian creed, but to inculcate the great principles of morality and religion. "The government of the School is intended to be mild and generous, but firm and decided. An effort will be made to excite in the mind of the pupil a love of study, and a determination to act, and to act aright, and the presence of those who are not, and cannot be influenced to be, thus inclined, is not desired, and will not be tolerated."
In 1906 Vermont passed a law requiring all towns to provide advanced instruction either by maintaining a school or by paying tuition for their children to attend schools which already existed. The new law went into effect in April, 1907, and Thetford Academy appears on a list of approved Secondary Schools published the following year. From this time on the Academy gradually changed its curriculum to meet the broadening needs of a larger segment of the town's young people. The Academy's survival and growth in this century have largely been due to the dedication and lifelong effort of Carl Anderson (left), principal for 36 years (1925-1961), his successor Ruel Barrett, who served for 16 years (1961-1977), and Frederick G. Torrey, head of school for 12 years (1977-1989). They built a new campus after the loss by fire of the original building, expanded to include the seventh and eighth grades, constructed the Arts Building, initiated a commitment to computers, and developed educational programs to serve the needs of the children of the townships which had designated or used the Academy as their High School. The 1967 By-Laws state: "The school shall be known as a 'Junior-Senior High School' and shall provide an adequate course of instruction for the proper education of students at the Junior High School and Secondary School levels."