Yet another report shows that Boston Latin School, the historic crown jewel of public education in Boston, has a diversity problem. The city’s half-measures haven’t made much of a dent, and it’s time for Mayor Marty Walsh to show some political courage by allowing the school department to tackle the roots of the gap: the standardized test that forms the cornerstone of the exam-school admissions process.

First, the problem: Right now, black students represent 8 percent of the student population at Boston Latin, while they account for 34 percent of the district’s student body at large; the corresponding figures for Latinos are 13 percent and 42 percent. Those numbers are embarrassing.

Thus far, the city’s response to concerns about diversity has been to expand test-prep classes, providing students from disadvantaged backgrounds the same boost wealthy families often give their kids. But it’s the test itself — which, along with grades determines admissions — that appears to be the problem.

Read the full editorial on the Boston Globe website.