On Two Kinds of Manipulation for School Choice Problems

Many school districts in the US employ centralized clearing houses for the placement of students to public schools. A popular mechanism from two-sided matching theory, the Gale-Shapley student- optimal stable mechanism, has recently replaced two defi…cient mechanisms that were in use in NYC and Boston. An important potential threat against any school choice mechanism is the tendency of schools to circumvent the procedure via two kinds of strategic manipulations introduced by Sönmez (1997, 1999): manipulation via underreporting capacities and manipulation via pre-arranged matches. This paper studies the extent of the vulnerability of a school choice mechanism, and in particular, that of the student-optimal stable mechanism, to the two manipulations, and identifi…es conditions under which they can be avoided.