Skip to main content

Redefining ‘Fairness’ Could Improve K-12 School Assignment Outcomes

statue of the scales of justice
Photo credit: Michael Coghlan. Shared under a Creative Commons license.

Researchers are putting forward a definition of “fairness” that could be used in public K-12 school assignment processes to get more kids into their preferred schools – without moving any kids into less preferred schools.

In many parts of the U.S., parents or guardians can report their public school preferences to the school system. Public school systems then use complex models that make use of these preferences and other variables to determine each child’s school assignment. These determinations rely on clear definitions of fairness, which can be used to ensure that no student’s priority for a given school is violated in favor of another student.

“What we’ve found is that there is definition of fairness that can be used to ensure that every student’s assignment would either be the same or better,” says Thayer Morrill, co-author of a paper on the work and an associate professor of economics at NC State. “To our way of thinking, if we can make more people happy without hurting anyone, the previous approach was wrong.”

One way of articulating the new definition is to say that a student can only object to not receiving a school assignment if it was possible for him or her to get that school assignment. Another way of explaining the definition would be to say: “a set of assignments is legal if and only if any assignment outside the set has justified envy with some assignment in the set and no two assignments inside the set block each other via justified envy.”

Confused? Don’t feel bad. This is pretty obscure stuff. Experts can read the paper for details. Everyone else: bear with me here.

Previous work on efficiency has shown that it’s possible to get more students into their desired school without disadvantaging everyone. For example, economist Al Roth and his collaborators showed that it was possible for 7% of students in New York City public schools to get into a more desired school, without sending one student to a less-desired school.

However, that work was not implemented, because it didn’t satisfy the definition of fairness the school board had to comply with in order to avoid legal jeopardy.

“Our work is on fairness, not efficiency,” Morrill says. “However, our definition of fairness is logically rigorous, results in improved school assignment outcomes, and we think would survive any legal challenge.”

The paper, “(Il)legal Assignments in School Choice,” was published in 2019 in the Review of Economic Studies. Lars Ehlers of Université de Montréal is corresponding author of the study.