Trade-offs in School Choice: Comparing Deferred Acceptance, the Naive and the Classic Boston Mechanism

Abstract

The three most common school choice mechanisms are the Deferred Acceptance mechanism (DA), the classic Boston mechanism (BM), and a variant of the Boston mechanism where students automatically skip exhausted schools, which we call the adaptive Boston mechanism (ABM). Assuming truthful reporting, we compare student welfare under these mechanisms both from a conceptual and from a quantitative perspective: We first show that, BM rank dominates DA whenever they are comparable; and via limit arguments and simulations we show that ABM yields intermediate student welfare between BM and DA. Second, we perform computational experiments with preference data from the high school match in Mexico City. We find that student welfare (in terms of rank transitions) is highest under BM, intermediate under ABM, and lowest under DA. BM, ABM, and DA can thus be understood to form a hierarchy in terms of student welfare. In contrast, in (Mennle and Seuken, 2017), we have found that the same mechanisms also form a hierarchy in terms of incentives for truthtelling that points in the opposite direction. A decision between them therefore involves an implicit trade-off between incentives and student welfare.