Many are now asking whether that confidence was misplaced.
With the revelation this week that more than 900 students — one-third of last year's high school graduates — should not have been awarded diplomas because of truancy and other problems, the school system has turned virtually overnight into an embarrassment for the city and its elected leaders, who are publicly re-examining their assumptions about the system's progress.
The FBI, U.S. Education Department and D.C. Office of the Inspector General are investigating the school system, with a focus on Ballou High School, where questions about graduation rates first emerged, according to a current and a former D.C. government employee familiar with the probe.
The scandal is reverberating far beyond the District, as a busy cottage industry of education policy analysts takes stock of whether the inflated graduation rates point to basic flaws in reforms the city has exported to other struggling school districts.
Jack Jennings, founder of the Center on Education Policy and former general counsel for the House of Representatives Committee on Education and Labor, said school leaders across the country are paying "a great deal of attention" to what is happening in the District — especially because high graduation rates have been so heavily emphasized by reformers as a measure of success.
"This has been identified by several presidents in a row, and by numerous governors and state legislators, as the primary goal in education," Jennings said. He said the District's problems with graduation rates could ultimately be a moment of reckoning similar to the 2009 cheating scandal in Atlanta's public schools, which led to racketeering convictions for 11 teachers who tampered with standardized test scores to hide students' poor performance.
That scandal, Jennings said, "caused educators around the country to pause a moment" in the headlong pursuit of better metrics.
American Federation of Teachers President Randi Weingarten said the D.C. graduation problems illustrate the "toxic" consequences of overreliance on potentially misleading measures of success.
"It's yet another wake-up call about this flawed logic that metrics are the be-all and the end-all," Weingarten said. "When these metrics and targets become more important than learning, they create a fertile climate, an environment, for scandal and for abuse."
At the local level, parents and activists are trying to gauge the extent to which the school system's vaunted transformation may have been overhyped.
"This absolutely is a challenge to the image that D.C. has burnished as a leader in urban education reform — there's no question," said Conor Williams, a senior researcher in the education policy program at the New America Foundation and father of two children in D.C. charter schools. "It's clear that there are systemic problems around rigor, around accountability and around transparency."
But Williams said those problems should not distract from real improvements that have taken place since the District embarked on its school-reform project in 2007. He pointed to the system's prekindergarten program, which provides near-universal schooling to 3- and 4-year-olds, and to the reshaping of D.C. Public Schools as a "working, functional bureaucracy." The graduation scandal was an "embarrassing situation around only one metric," he said.
Longtime backers of the city's reform policies say they fear the graduation scandal could distract from other gains — such as improving standardized test scores and increasing enrollment — and supply ammunition to critics.
"My worry is that elected officials and advocates with their own agenda might try to score political points off this story, rather than embracing the nuances of school improvement," said Catharine Bellinger, director of the D.C. chapter of Democrats for Education Reform. "Progress is never going to be linear. It's fast in some areas and slow in some others."
Such concerns might be premature: There have been no calls from any D.C. public officials to repeal the main tenets of education reform put in place by former mayor Adrian Fenty and former schools chancellor Michelle Rhee — such as mayoral control of the public schools and the linking of educators' salaries and job security to numeric measures such as student test scores and graduation rates.
In fact, Mayor Muriel E. Bowser (D) has responded to the crisis by saying those measures will be more rigorously assessed and enforced.
There is little evidence yet that problems in the schools will do short-term political damage to Bowser, who is in the midst of a reelection campaign.
With just four months until the Democratic primary — which typically determines the general election winner in overwhelmingly Democratic D.C. — Bowser is sitting on a $2 million war chest and has no serious opponents.
The only potential challenger, former mayor and current D.C. Council member Vincent C. Gray (D-Ward 7), could be poorly positioned to attack Bowser on school problems, since some are blaming Kaya Henderson, the chancellor Gray appointed in 2011, for fostering an organizational culture that overemphasized performance data, creating pressure on school administrators to fudge graduation rates.
"If it is a Bowser versus Gray race, neither one of them have much to say," said RiShawn Biddle, editor and publisher of the school reform commentary site Dropout Nation. "And if anything, Bowser will get the credit for cleaning things up."
The changed political dynamic surrounding public education in the nation's capital has nevertheless been evident in recent weeks, as Bowser and Antwan Wilson, whom she installed as chancellor last year, have felt compelled to defend a school system that for years has provided bragging rights, not political headaches.
"Let's make no mistake about it: We are in a very different place with our public schools," Bowser said in a briefing to D.C. Council members Tuesday on the graduation scandal. "I feel very confidently that our public education in the District advanced dramatically in the last 10 years. We see more of our families coming back to our schools. We see significant improvement at the elementary levels."
There have always been flaws in the argument for the District's education reform experiment as an unalloyed success. The city continues to have some of the nation's widest achievement gaps between low-income students and their more affluent peers. Some have attributed improved standardized test scores to changing demographics — arguing that gentrification, not better policy, has boosted performance.
Max Eden, a senior fellow at the conservative Manhattan Institute, said the revelation of systemically inflated graduation rates is vindication for opponents of metrics-based reform who have warned that students would suffer as their teachers and principals gamed the numbers.
"I think it poses a profound problem for the education reform movement, which held D.C. to be its star child," Eden said.
Questions about improperly awarded diplomas — first disclosed in a report on Ballou High School by WAMU-FM (88.5) — come on the heels of two other scandals in the past nine months that called into question the integrity of school policies and performance data.
In July, The Washington Post reported that the school system had misrepresented its student suspension rates, barring many students from attending high schools because of behavior problems without formally marking them as suspended.
In May, The Post reported that Henderson, the former schools chancellor, had helped well-connected parents — including two senior Bowser aides — skirt the requirements of a lottery system that is supposed to ensure a fair shot at the best public schools for all families.
Many questions are still unanswered about the District's graduation rate, which in 2017 was ostensibly at a record high of 73 percent. A city investigation released Monday found that about one-third of those students should not have graduated because they missed too many classes or improperly took make-up classes.
Teachers felt pressure from school administrators to pass students, the report found, but it is unclear how long that practice has been common and whether there was a deliberate effort to manipulate graduation numbers from top school officials.
Responsibility for the situation is also muddied by the school system's leadership changes over the past 18 months: Henderson stepped down in September 2016 and was succeeded by an interim chancellor, John Davis, who was replaced by Wilson last February — about four months before the class that is now under scrutiny graduated.
Wilson, with Bowser's backing, has pledged to retrain principals and teachers on the city's graduation policies and begin a centralized review of graduates' academic transcripts to ensure that they are eligible to receive diplomas. By 2022, he said, schools citywide will also hold end-of-course exams to assess whether students mastered material in core subjects.
But after the latest scandal, future claims to have fixed this problem — and others in the schools — could be met with more intense scrutiny than in the past.
"When we are told repeatedly that numbers are rising and progress that we are making is fantastic and wonderful, and then we find out it may be based on faulty or fudged information," said D.C. Council member Mary M. Cheh (D-Ward 3), "that makes one skeptical."
Moriah Balingit and Perry Stein contributed to this report.