The study, authored by Bergman and Isaac McFarlin, a professor of education at the University of Florida, examines the beginning of the school-choice process: inquiries about how to apply. In a randomized test, the researchers sent emails from fictitious parents to more than 6,000 charters and traditional public schools in areas with school choice. “Each email,” Bergman and McFarlin wrote, “signaled one of the following randomly-assigned attributes about the student: their disability status, poor behavior, high or low prior academic achievement, or no indication of these characteristics.” The pair wanted to see whether schools provided the same information to all parents, regardless of any difficulties alluded to in the emails.

Ultimately, Bergman told me, they found that the schools they emailed are less likely to respond to students who are perceived as “harder to educate.” The charter schools, he added, were “particularly less likely to respond to students with a particular [individualized educational plan]”—meaning students who have a special need that would require them to be taught in a separate classroom. This “cream-skimming,” or providing information only to high-value students, is a “key source of potential inequality,” Bergman said.

Read: How to rile up education debates with one word

An easy takeaway from the report, McFarlin told me, would be that “charter schools discriminate against special-needs kids,” but that would be an incomplete assessment, since the schools they emailed replied to the parents of any student with any disadvantage—behavioral issues, low grades, or special needs—at similar rates. Now that researchers know whether schools responded to the emails, the next step is digging into the responses to see if they are actively discouraging certain students from applying.

In the meantime, Bergman and McFarlin hope that this sparks a conversation about how the subtle discrimination of not responding to an email can create an information gap for families in the application process. School choice, with a goal of equitable access, could work, they say, but only if it truly allows the students to choose schools, rather than allowing the schools to choose students.