Around 1940, the Southern Association Study in Secondary Schools and Colleges and the Secondary School Study of the Association of Colleges and Secondary Schools for Negroes implemented cooperative educational experimentation in the American South. This was a progressive education method for improving schools exemplified in the national Eight-Year Study. The research detailed here reconstructs the work of the two southern studies as it occurred in tandem and in connection with the Eight-Year Study and the General Education Board. The white Southern Study utilized the progressive cooperative study as a clinical technique largely divorced from democratic ideals. The black Secondary School Study leveraged the progressive cooperative study as a means to democratize African American education in the South. The findings reported here confirm and complement conclusions in the historiography of African American education, extend historical perspectives on the Eight-Year Study, and contribute to an understanding of how progressive education was interpreted and translated into practice.