Monday, April 22, 2013

Priorities vs. Precedence in School Choice in Boston

School choice plans in many cities grant students higher priority for
some (but not all) seats at their neighborhood schools. This paper
demonstrates how the precedence order, i.e. the order in which
different types of seats are filled by applicants, has quantitative
effects on distributional objectives comparable to priorities in the
deferred acceptance algorithm.

While Boston's school choice plan
gives priority to neighborhood applicants for half of each school's
seats, the intended effect of this policy is lost because of the
precedence order. Despite widely held impressions about the
importance of neighborhood priority, the outcome of Boston's
implementation of a 50-50 school split is nearly identical to a
system without neighborhood priority.

This paper formally establishes that
either increasing the number of neighborhood priority seats or
lowering the precedence order positions of neighborhood seats at a
school have the same effect: an increase in the number of
neighborhood students assigned to the school. The papr shows that in
Boston a reversal of precedence with no change in priorities covers
almost three-quarters of the range between 0% and 100% neighborhood
priority. Therefore, decisions about precedence are inseparable from
decisions about priorities.

Transparency about these issues--in
particular, how precedence unintentionally undermined neighborhood
priority--led to the abandonment of neighborhood priority in Boston
in 2013.

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