“…The families belong to two different types, nonwhites or blacks (type B) and whites (type W) whose respective 7 The inefficiency of segregation, the need for qualification, and the de facto emergence of "gray areas" (mixed neighborhoods) boosted desegregation in schools even before the abolition of Apartheid laws. For an interesting presentation of school desegregation and subsequent issues in South Africa, see Naidoo [22,23], Tikly [30,31], and Penny et al [25]. 8 All of these assumptions are very standard in urban economics, and relaxing them does not alter our main conclusions (see Fujita [16]).…”