The John Dorr Nature Laboratory, a 275 acres (111 ha) campus in Washington Depot, Connecticut, serves as the school's outdoor and community education center.

[3] The school was founded in 1887 by Nicholas Murray Butler as a co-educational experimental and developmental unit of Teachers College at Columbia University.

He used each of his positions to proclaim that every person, regardless of their background, should receive a public education based on the principles and practices of a free society.

There is also the John Dorr Nature Laboratory, located on 275 acres (111 ha) of land in Washington Depot, Connecticut, used for extended field trips for classes of students starting in second grade and an orientation program for new students entering the Middle or Upper Divisions.

[7] Starting in eleventh grade, students have more flexibility with their requirements and can choose from courses in biotechnology, calculus, economics, ethics, psychology, religion, political philosophy, United States legal history, art history, and statistics, among other elective classes.

[8] All students are required to take a swim test and American Red Cross CPR certification in order to graduate.

In the Lower and Nursery Divisions, there is an annual "Caring-in-Action" day dedicated to community service that students and their families can attend.

[9] Admission is selective with decisions based on recent grades, an interview, an essay, and the candidate's score on either the ISEE or SSAT test.

[11] In 2024, the Niche survey ranked Horace Mann the fifth-best private high school in the country.

[14] On June 23, 2012, The New York Times reported that Tek Young Lin, Horace Mann's former chaplain who also served as an English teacher and track coach, admitted that he had had sexual relations with several male students.

[16] The charitable organization helps alumni with their therapy costs and addresses related issues in the broader community.

[14] In March 2013, The New Yorker published an article discussing sexual abuse allegations against former Horace Mann English teacher Robert Berman.