KANSAS CITY, Mo. — John Covington arrived here two years ago with the promise of transforming a district that had become synonymous with the failures of urban education. He even managed to win support for his drastic recommendation to shut down nearly half its schools, saying it was a necessary step to achieve desperately needed stability.

Stability is not something the district had enjoyed for some time. In the previous four decades, the title of superintendent of the Kansas City Board of Education rotated through more than two dozen people, during which time reforms were offered and abandoned as student enrollment and performance declined.

And this summer, while negotiating a new contract, Covington talked of continuing with what has been one of the most aggressive turnaround efforts in the nation.

“It’s a big day for me, inasmuch as I have outlived the 18-month average of staying power and begin my third year in Kansas City,” he said at the beginning of his state of the schools address .

Then last week, not long after students returned to classes, Covington abruptly resigned.

School board members said he told them he had not applied or interviewed for any jobs. But after several days of lobbying to get him to stay — the board refused to accept his resignation, and The Kansas City Star ran editorials urging him to reconsider — Covington made news again by accepting a high-paying job as the first chancellor of a statewide initiative intended to improve Michigan’s failing schools, starting with those in Detroit.

The move highlighted one of the less-publicized problems facing urban education — the average tenure of a big-city superintendent is 3.6 years, according to the Council of the Great City Schools. And at least 15 major school districts have vacancies in their top leadership post, the council said.

Several school board members here lamented that needy districts have to fight with each other for administrators.

“Urban education is tough, and the talent is scarce. It has always been that way, and it always will be,” said Airick West, the school board president, who had a troubled relationship with Covington that some suggested encouraged the departure.

Covington declined to comment but said in a statement last week that he apologized “for the difficulties for which my resignation created.”

Despite the rancor the resignation has caused, school and community leaders have pledged to stick with the policy changes laid out over the past two years, rather than turning over the district to a leader with another vision.

When Covington arrived, the district, facing a huge budget deficit, had just 17,000 students in 61 schools that collectively were more than half empty.

His solution — closing 26 schools and cutting a third of the district workforce — passed by one vote on the school board with significant community support. His many other initiatives also passed, including grouping elementary school students by skill level rather than by grade, combining middle and high school and bringing in more than 150 Teach for America recruits.

The district balanced its budget for two straight years. And city residents, many of whom long ago had lost faith in school leaders, rewarded Covington with a school board more supportive of his agenda.