The Freedmen's Bureau helped to reform education in the South mainly by helping to create a system of public education in that region.
Before the Civil War, there was very little in the way of public education in the South. Southerners typically felt that education was something that should be provided by the family or the church. This meant that it was mostly well-off white people who got educated.
During Reconstruction, the Freedmen's Bureau helped to create schools for the freed slaves. By doing so, they also helped to create the idea that state governments should be responsible for providing education not only to blacks but to whites as well.