This paper addresses the question of how diversity has been dealt with in the 20th century since the formal inauguration of social studies as part of the U.S. public school curriculum. Given space constraints, the many historical reasons for change in the treatment of diversity is outlined in the paper in broad terms. Likewise, the larger subject of diversity within the social studies curriculum is limited to three dimensions: (1) race; (2) ethnicity; and (3) gender. The paper points out that defining difference in these categories is a strategy designed to focus on several concerns pertinent to the field today. However, this approach could also be employed in looking at other facets of difference in social studies curriculum, such as religion or class. It notes that the social studies emerged during the period 1890-1920, during which nativist and racist reactions to the challenges of emancipated slaves, alien newcomers, and unsettled gender relations were all deeply implicated in refashioning the educational enterprise. The paper attempts to articulate how the social studies curriculum has responded to the press of cultural, racial, and gender differences since the birth of the field. It also invites other researchers to test the hypotheses offered in future considerations of this subject. (Contains 72 notes.) (BT)