Nationally, 18 percent of teachers are people of color—including African Americans, non-white Hispanics, Native Americans, and Asians—according to the authors of an August 2016 report published by the Brookings Institution. The report, which focuses on African American and Hispanic teachers, projects that, as 1 million white teachers exit the profession, 300,000 African Americans and 600,000 Hispanics would need to join it for the demographic makeup of the teaching force to reflect that of the youth population.

Michael Hansen, a senior fellow at the Brookings Institution and the director of the Brown Center on Education Policy, is among a number of experts who say minority students may be underperforming because they don’t have role models in positions of authority who look like them. “And of course, being young kids going through schools, the person in any position of authority is teachers,” Hansen said.

Research has documented other ways that a teacher’s race can affect student performance. A March 2016 study by Johns Hopkins University showed that black teachers are more likely to have higher expectations for their black students; white teachers, for example, were almost 40 percent less likely than their black counterparts to expect black students to finish high school.

For years, education reformers, particularly in the charter-school world, have focused on recruiting the best teachers. Many charters have started their own training programs to ensure top quality.

But, increasingly, schools that serve high populations of minority students, such as PUC Schools, are taking note of the research showing that the race of teachers matters and have begun to prioritize diversity along with that top quality. They’re discovering that their own alumni are the perfect pool to draw from, since former students inherently reflect a school’s racial and ethnic makeup. An added bonus: They often have deep roots in the local community and may be more likely to stay in the job, which can help address the chronic problem of high teacher turnover at many urban schools.

Mastery Charter Schools serves over 13,000 students at 22 schools in Philadelphia and in Camden, New Jersey. As the school system has expanded, it has had to hire hundreds of new teachers to work in its so-called turnaround schools—failing schools that it hopes to resuscitate. Recruiting alumni is one way to ensure teachers are committed to taking on the challenges of working in turnarounds, according to Courtney Collins-Shapiro, the chief innovation officer at Mastery.

Last year, Mastery started a residency program to train and mentor new teachers as they pursue a master’s degree with Relay Graduate School of Education. Of the 60 resident teachers currently enrolled in the program, nine are Mastery alumni, Shapiro said.