The Limits of Rank-Dependent Priorities in School Choice

Abstract

Many school choice mechanisms give students higher priority at schools they rank highly and aim to reward students' eagerness. This paper studies whether a centralized mechanism can incorporate such rank-dependent priorities while preserving truthful reporting. I consider a mechanism that jointly specifies how reported preferences modify schools' original priorities and how assignments are determined based on the modified priorities. I require the modification rule to satisfy rank monotonicity and the resulting matching to be stable with respect to the modified priorities. These two requirements jointly capture the policy objective of rewarding eagerness. My main result shows that any mechanism satisfying these requirements as well as strategy-proofness is outcome equivalent to the student-proposing Deferred Acceptance mechanism using the original priorities. Thus, if eagerness affects the outcome while the rank-dependent policy goal is maintained, the mechanism must be manipulable.