From 1858 until Princeton Public Schools integrated in 1948, your Witherspoon Street School for Colored Children educated Princeton's African-American children. The school began in the building still standing at 184 Witherspoon Street, and as enrollment grew it moved in 1909 to 35 Quarry Street. That Quarry Street building was expanded in 1939 and again in 1966, which gave it the appearance you see today.
The former school has since been turned into an apartment building, and it was added to the National Register of Historic Places on March 9, 2005, for its significance in education. Architecturally it is Colonial Revival in brick, with an ornate cupola centered on the roof. In 1948 the Journal of Negro Education noted that this school had empty spaces while the school for white children was overcrowded — a striking observation to carry with you as you look around.
You can see how those changes are visible from here. Notice the brickwork and the Colonial Revival details, then the ornate cupola centered on the roof.