Outgoing D.C. schools chancellor Kaya Henderson on June 29. (Marvin Joseph/The Washington Post)

IT WAS fitting that on the same day new test scores were announced for D.C. students, the first community forum on the search for a new schools chancellor was held. The results offer a scorecard for an improving, but still challenged, school system — and a job description for its next leader. It is crucial that the District, in selecting a successor to outgoing chancellor Kaya Henderson, stay on track with reforms that have helped schools improve and that are key to fixing the problems that remain.

Results released Tuesday from the second year of national standardized tests linked to the Common Core academic standards showed overall improvement in English and math. The increases were slight (0.6 percent in English and 3 percent in math), with still only about a quarter of students deemed proficient. But Ms. Henderson was right in characterizing the “slow, steady progress” on this demanding new test as further evidence of school improvements and investments paying off for D.C. students.

Most encouraging was that, aside from what officials see as an anomaly in test-taking at normally high-performing high schools, there were gains across all grades and most student subgroups. Black, Hispanic, special education, English-language learning and low-income students all improved in both English and math, and there were gains in schools in every ward of the city. Reforms in curriculum, instructional time and teacher hiring, training and evaluation are paying off. Students over the past decade have shown consistent gains on the national exam known as NAEP. Enrollment has increased and graduation rates have improved.

Everyone — starting with Ms. Henderson — acknowledges the daunting challenges still facing the system. Foremost is that a majority of students are not proficient in core subjects and that the achievement gap between minority and white students persists, issues that threaten to become even more acute with changing city demographics and the accompanying income divide. So, what’s next?

A decade of school reform and the years of revolving school superintendents and school failure that preceded mayoral control in 2007 teach that there are no easy answers or overnight solutions. The District has gotten as far as it has thanks to stable leadership from Ms. Henderson and her predecessor, Michelle Rhee, both of whom attacked problems by sticking with things proven to work. The value of such continuity should be uppermost in the minds of the committee members conducting the search for Ms. Henderson’s replacement; of Mayor Muriel E. Bowser (D), who hopes to name her choice for chancellor by mid-October; and of the D.C. Council members who must sign off on this critical appointment.