D.C. Mayor Muriel E. Bowser (D) in Washington on Aug. 9. (Brian Snyder/Reuters)

FROM THE uproar over graduation practices to the scandal over the improper high school placement of the schools chancellor’s daughter, there was plenty of bad news about the District’s public school system last school year. So it was reassuring to learn that students nonetheless showed improvement in achievement. As a new school year begins this week, the city must avoid the missteps and redouble its efforts to sustain the progress of recent years and meet the formidable challenges that still confront the system.

Standardized test results for the 2017-2018 school year released last week showed improvements in English and math by public school system students at every grade level tested and across neighborhoods, races and income levels. There was a 3.2-percentage-point increase over last year in English and 3.1-point increase in math, outpacing the state average, which included results from public charter schools, which also showed improvements. It was the third consecutive year of growth on PARCC, the rigorous assessment for college and careers testing that the city started using in 2015 with the introduction of a more challenging curriculum.

To be sure, as officials stressed in announcing the results, there is still much work to be done, with some two-thirds of students still not proficient in English and math and a wide achievement gap between white students and students of color. But the steady gains — including notable shrinkage of the achievement gap in English — underscore the efficacy of school reform started a decade ago and serve as a rebuke to critics who would try to use the recent school scandals to undermine mayoral control. By expecting more from both teachers and students, and with a long period of stability under the leadership of Michelle Rhee and Kaya Henderson, officials put in place a strong foundation that must not be abandoned.

Now Mayor Muriel E. Bowser (D), almost certain to be reelected to a second term, needs to step up her game on education. She must show more urgency in staking out an agenda to solve the challenging problems that persist. Most critical, of course, will be her selection of a permanent schools chancellor and deputy mayor for education. Hopefully she has learned some lessons from the events surrounding then-Chancellor Antwan Wilson’s ill-fated tenure, and the District will once again have stable and steady school leadership.