The Horace Mann elementary school at 11th Street and Jennings Avenue was built on a 1.05 acre plot in 1907 for $40,000. The city deeded 6 lots along Jennings between 11th and 12th Streets to the district on May 15, 1909.

A 1929 addition to the campus, consisting of 0.35 more acres of land from two lots at the corner of 12th Street and Keeler Avenue, was once valued at $16,086.

Just southeast of Horace Mann on the northwest corner of 12th and Keeler was the original city hospital, which had opened in 1906 as a 15-bed two-story facility. It was later expanded with an east office addition, front porch, and side porch. The hospital building was sold to the county in 1918 and superseded by Washington County Memorial Hospital in 1922.

In 1929 the district acquired the two lots where the original hospital had stood. They were used to expand the playground south of Horace Mann so that it extended from Jennings to Keeler. It is unclear when the old hospital building was removed.

In 1952 all-purpose and special education rooms were added for $87,803 on the north end of the original building.

The school was closed in June 1968 and the original building and the 1929 addition were razed in 1969. The 1952 addition was remodeled into the district Media Center at a cost of $63,860 in 1970 and in 1973 the neighboring property at 1115 S. Keeler was purchased for $7,466 to join with the two lots, which once had the city hospital and later were the playground, to become part of expanded parking along Keeler Avenue.

In 1974 the 1952 addition was remodeled and expanded into the Education Service Center at a cost of $237,128. Some interior finishes were updated in the late 1990s and in 2016-2017.

In October 2020 the Board of Education approved a $876,800 bid from Rick Scott Construction for a 2,500 square foot addition to the south end of the existing building and the renovation of about 1,000 square feet of existing interior space so that the district's Technology Services department could be relocated before July 2021 from rented space at the Will Rogers Complex. The addition included an office and warehouse with a freight dock, reworking of the south parking area, and repaving of the alleyway. The former accounts payable suite and garage in the 1974 structure were renovated into a workroom and server room, respectively. The entire exterior was repainted, and new signage was installed on the west façade with the lava rock sheathing replaced by white-painted brick to match the new brick addition.