ANN ARBOR—While there has been much debate across the country about the benefits and drawbacks of public school choice, an often overlooked issue is the lack of a fair and objective method for assigning students to schools both within and outside their districts, says a University of Michigan researcher.

“By now, several cities have adopted school choice plans,” says Tayfun Sonmez, U-M assistant professor of economics. “While all of these plans have their protocols and guidelines for the assignment of students, none of them has a rigorous procedure.

“This offers opportunities for manipulation and results in appeals by parents who are unsatisfied with the school assignments of their children. You need to have a set of procedures that are very explicit, with rules.”

While previous education literature provides guidance for the design of such mechanisms, but not specific methods, Sonmez and colleague Atila Abdulkadiroglu of the University of Rochester propose a student assignment plan to fill this gap.

The researchers say that their “top trading cycles mechanism” is simple, realistic to implement and easily explainable to parents. Moreover, it is flexible enough to adhere to state laws that may require different priorities at different schools, including giving preferences to students who live in a school’s attendance area, whose siblings already attend a particular school, or who require special programs offered by certain schools.

In addition, their plan can be easily modified to respect racial, ethnic and gender balances, and to ensure the balanced instructional capacity of a school.

The plan, they say, works like this: first, in accordance with state laws, priority ordering of all students for each school is announced (based on priorities stated above); next, students and their parents submit a preference ranking of schools; and finally, student assignments are based on priorities and preferences.

Assignments are first made by finding all the students who have the highest priority for at least one school, the researchers say. These high-priority students can either keep their assignments or trade them with students who have the highest priorities elsewhere (in essence, these students would swap places). Once these assignments are made, then the process would continue in the same way for the remaining students.

Of course, the researchers say, in order to break ties for students with identical priorities, a lottery in the presence of community representatives should be conducted to determine priority ordering.

“The top trading cycles mechanism creates a ‘virtual marketplace,’ with students entitled to trade their priorities,” Sonmez says. “Students rank all schools and once the policies concerning school priorities are announced and these priorities determined, the final outcome is deterministic and does not leave any room for manipulation.”