The American Historical Association's (AHA's) Commission on the Social Studies was a compilation of prominent scholars who, from 1929 to 1934, investigated social studies education in American public schools in order to provide some cohesive recommendations for teachers. The AHA Commission had a controversial ending, with one of its members, University of Iowa curriculum professor, Ernest Horn, leading a protest against the Commission's final summary volume. This historical inquiry unveils that the cause of controversy revolved around the use of objective testing (now known as standardised testing) in the social studies curriculum, resulting in two duelling camps within the Commission: those who were against the use of objective testing and those who promoted its use. The Commission, therefore, became the battleground for one of the first debates on the role of standardised testing in the school curriculum. (Contains 2 figures and 100 footnotes.)