A major finding of the pioneering empirical research on the American student movement of the 1960's was that students who engaged in campus protest were primarily raised in "humanistic," liberal, middle-class families. Based upon these data, the development of student activism was seen as growing from the almost unique aspirations and values of a small proportion of college and university youth who were particularly sensitive to and unable to accept authoritarian institutional structures and social injustice because of their family backgrounds. More recently, with the enormous growth of campus unrest, this theory of student activism has been challenged. A study conducted at the University of Wisconsin in 1968 by one of the authors indicates that there has been a significant change in the social base of the student movement since the early and mid-sixties. This evidence, together with other research findings which are consistent with the thesis of a changing social base of activism, suggest that the "family socialization" theory is becoming less adequate as an explanation of what has become a mass student movement. The extension of student protest to larger sectors of the student population is indicative of a growing "class" consciousness among students which has its basis in a general cultural and political crisis combined with the growing segregation, "proletarianization," and repression of youth. The implications of these emerging social sources of the student movement for the radicalization of a "new" working class and the "territorialization" of youth revolt are considered.