This paper addresses world-system/dependency theories of differential economic growth among nations. We grant that such perspectives have considerable analytic potential but have serious reservations concerning their current empirical status. Our croticisms focus particularly on the absence of evidence on the theoretically specified structural positions (core, semiperiphery, periphery) in the world system and the dynamic relations among them. After indicating why extant quantitative studies that claim to represent "position" are inadecuate, we propose that blockmodel analyses of social structure through multiple networks address world-system formulations far more appropriately. We present a blockmodel of the world system circa 1965 that is based on four types of international networks: trade flows, military interventions, diplomatic relations, and conjoint treaty memberships. While we invite replications with additional network data, this blockmodel provides strong evidence for a core-semiperiphery-periphery structure. We then report regression analyses of the efects of these structural positions on nations' economic growth (change in GNP per capita) from 1955 to 1970. Net of other plausible determinants, these effects are large in magnitude and entirely consistent with world-system/dependency theories theories. Further analyses reinforce the interpretation of these findings as the structural, accumulative advantage of location in the core over that in the periphery. Substantively, our results that exogenetic theories of economic growth are even more powerful than previous analyses have indicated. Moreover, they demonstrate the natural wedding of a conceptual framework (the world system) with an empirically grounded theory of social structure (blockmodel analysis), which has applicability much beyond issues of economic growth.