School assignment and school effectiveness.

• Author: Pathak, Parag
• Position: Research Summaries

A growing number of U.S. households have the opportunity to send their children to public schools outside of traditional neighborhood boundaries. Over the last decade there has been a proliferation of research on the design of centralized choice systems intended to make it easier for children to exercise choice. Millions of students have been assigned to schools using mechanisms either directly or indirectly inspired by academic work.

In recent research with several co-authors, I explore the equity, efficiency, and incentive properties of these choice systems. Aside from these properties, centralized assignment generates valuable data and quasi-experimental variation that can be used for evaluation of various educational practices and policies. I have worked with several researchers to exploit this variation to study productivity differences between schools and school models.

Immediate Acceptance

One of the most common school assignment systems is based on the concept of immediate acceptance: when applicants apply to a school, they are offered a seat immediately if they qualify. A mechanism based on this principle was in place in Boston until 2005, and hence it is commonly known as the Boston mechanism. (1) A large number of Local Education Authorities in England also employed this mechanism, called First Preference First.

One issue with this mechanism is that applicants do not have the incentive to rank their desired schools truthfully. That is, ranking a competitive school first may harm a student's chances at lower-ranked schools, creating strategic pressure on the applicant. Should an applicant take a risk at the school she really wants, or instead rank a safe choice first ? In work with Tayfun Sonmez, I show that if families do not understand these incentives and rank their choices truthfully, then sophisticated families who understand the rules of the game benefit at the expense of the unsophisticated. (2)

The poor incentive properties of immediate acceptance systems led authorities in Chicago to abandon their allocation scheme for the city's elite selective high schools in 2009. Officials in the Chicago Public Schools (CPS) observed that students with higher test scores were denied admission to their second-choice school, even though they had higher scores than students who ranked the school first. After eliciting preferences from more than 14,000 participants, CPS announced a new mechanism and asked participants to re-rank their choices. The new mechanism is a serial dictatorship where the highest-scoring student is assigned to her top choice, the next highest scoring student is assigned to her top choice among remaining schools, and so on. What is particularly surprising about this switch is that the new mechanism also did not have straightforward incentives because it limited the number of choices students could rank. Students could only rank four out of nine possible choices, necessitating strategic calculations on which choices to list and which ones to drop. In the subsequent year, they switched to a system with the same underlying algorithm, but allowed students to rank six schools.

A few years earlier, by an Act of Parliament, authorities in England outlawed First Preference First arrangements citing concerns that the procedure is unfair to unsophisticated participants. Following this legal ruling, many districts adopted variants of the deferred acceptance algorithm, known in England as Equal Preferences. (3) Using this procedure, first formally studied by David Gale and Lloyd Shapley in 1962, applicants start by applying to their first choice. Schools tentatively accept their preferred applicants up to capacity and reject the rest. Any rejected student applies to his next most preferred choice, and schools update their set of provisional acceptances by comparing these new proposals to students tentatively held over...