World-system scholars have traditionally emphasized the stability of the core/periphery hierarchy. However, prior network studies employing both categorical and continuous measures of world-system position reveal substantial mobility across time, whereby a number of developing states have become more integrated in the world economy over the past several decades. The developmental impact generated by such mobility remains unexplored. Using data on all commodities in the world trade network, I examine the presence and economic impact of world-system mobility across 110 states during the 1980-2000 period. First, I show that the continued upward mobility of "middle-tier" states from East Asia and the semiperiphery no longer contributes to the long-term trend of trade convergence, but began producing divergence during the final decades of the 20th century. Second, using difference models that control for lagged values, I find that world-system mobility positively affects economic growth, net of initial world-system position, capital and labor inputs, and other regional and economic characteristics. In fact, the magnitude of mobility's effect is substantially larger than that of initial world-system position and second only to initial human capital. These findings support a range of perspectives that are collectively useful for understanding the rapid economic growth of emerging states. (Contains 3 tables, 2 figures and 8 notes.)