Teachers and students are increasingly looking less like each other.

The divide between the share of teachers of color and the share of students of color grew by 3 percentage points over as many years, according to a new report from the liberal Center for American Progress.

Students of color make up almost half of the public school population, but teachers of color make up just 18 percent of that population nationwide. And the disparity is even larger in 36 states. It’s largest in California where 73 percent of students are nonwhite while just 29 percent of teachers are nonwhite.

There’s no single reason for the disconnect, according to the data brief. Disparities in college degree attainment mean that there are relatively fewer college-educated nonwhites than whites. More and more careers are opening up for nonwhites, meaning there are more fields for minorities to disperse to. And teachers often remain in the profession for years and years, so turnover can be slow in coming.

Teacher demographics can have an impact on students, CAP argues. Studies have shown that minority students fare better when taught by minority teachers and nonwhite educators may also find it easier to relate to students with whom they share a background.

States can do something about the disparity through increased funding for teacher preparation programs, CAP argues. And, it says, the federal government can offer assistance to low-income students interested in becoming teachers. The study is based on 2012 school staffing data and 2011 Common Core student population data.