The view that competition initiatives in education, such as Chile's introduction of vouchers, promote socioeconomic segregation in schools is questioned. Chile and Argentina have faced very different decentralization reforms, carried out within different regulatory frameworks, but have arrived at similar situations in terms of schools' socioeconomic segmentation. Vouchers are not an independent variable but an intervening one within the determinants of socioeconomic segmentation. (Contains 56 references.) (SV)