Julia Wilbur attended the dedication of the Sumner School on September 2, 1872:

After office went to dedication of Sumner School Building-Cor. 17 & M. Cost 50,000 & Lot 6,000--Fine & large. Various  speakers. Music.

A few months later, she reported that she was "impressed" when she visited the school in operation.

The school was built for African American students and honored Sen. Charles Sumner. Sumner was an anti-slavery leader in the Senate, to the point that a congressman from South Carolina assaulted him on the Senate floor in 1856. It didn't help that Sumner insulted the congressman's cousin in his general attack on slavery.

Through the years, Wilbur mentioned Sumner in her diaries--reading his speeches before the war, hearing him speak during the War in Congress and even paying him a visit (unfortunately, no description of the encounter), and expressing regret as he supported Greeley over Grant and eventually grew ill and died.

According to its website, the School hosted the first high school graduation for  African Americans in the U.S. in 1877. (This may refer to a graduating class, since individual students had graduated from high schools before this.) At first, although "separate," the Freedmen's Bureau was able to direct a fair amount of resources toward the education of young black students. Shortly after, the "separate" stayed in place, but without much in the way of keeping things at the same level offered to white students. It was used for a variety of classroom and office purposes.

As it happens, I attended classes and worked nearby in the 1970s. I recall (I think) a more or less abandoned building. Fortunately, it was renovated rather than torn down in the 1980s and remains in use as offices and meeting space.