The graduation rate in Prince George’s County dropped by more than four points for the Class of 2018, the largest one-year decline among Maryland school systems and another sign of fallout after a major diploma scandal erupted in 2017.

The on-time graduation rate in the suburban Washington system was posted at 78.47 percent, its lowest in four years and a blow to the successes once claimed by county leaders, according to figures released Tuesday by state officials.

But after two state-ordered investigations and a major effort to tighten controls on grading and graduation certification, the drop was not a surprise across the school system; some expected fewer graduates amid more rigorous practices.

The new numbers are the first look at graduation rates since changes were made. School officials said they have implemented 28 recommendations made by auditors.

“Under this stricter and more accurate measure, today’s graduation rate numbers present a difficult but necessary truth about the true progress we have made in preparing our students,” Monica Goldson, interim chief executive of Prince George’s public schools, said in a statement. “While the results do not show the progress we want, they do provide us with the accurate measure we need.”

Goldson said the system will remain vigilant “to ensure that the progress we made leaves our students, staff and community proud of their diplomas.”

Before allegations of fraud came to light, graduation rates in Prince George’s had been on the rise, improving more than 8.5 points over four years, to 82.7 percent for the Class of 2017.

In early 2017, Kevin Maxwell, who was chief executive of the Prince George’s school system at the time, paraded through high schools with pompoms and celebratory banners, cheering on the gains even as some observers had begun to raise concerns.

But later the same year, four members of a school board minority bloc said whistleblowers had stepped forward with allegations of grade tampering and transcript irregularities in county high schools.

A state-ordered investigation of county records and practices in 2017 found a number of students ineligible to graduate or lacking documentation to show they qualified.

A second investigation the next year found that the school system — Maryland’s second-largest — had improved many practices, but still had a major issue with absenteeism.

Raaheela Ahmed, who was a member of the board minority bloc that raised concerns, was pointed about the new state numbers.

“Sadly, this data shows how inflated our graduation rates became as a result of the grade fixing, unauthorized credit recovery programs and policy violations under the previous school system administration,” she said. “Now, because of the accountability procedures we’ve put in place, I believe our numbers are more honest.”

“We’re not where we could be, but at least we’re owning where we’re at,” she said.

Other board members expressed a mix of sentiments.

Alvin Thornton, chairman of the county board of education, said he was concerned about the significant decrease in the graduation rate but appreciated the system’s “laser focus” on strengthening practices.

Thornton noted remarks made in January by the president of the Maryland State Board of Education, who supported Goldson’s assertion that, following an overhaul of procedures, the system’s graduation and grading processes rate among the state’s best.

“I would almost guarantee that that’s true, not only because of the seriousness of purpose that you clearly bring to addressing this but because your county has been scrutinized in a way that none other has,” board President Justin M. Hartings said as Goldson and Thornton appeared before the state board.

Edward Burroughs III, a board member who led the minority bloc calling attention to the problem, said the system must focus foremost on student learning.

“It does a real disservice to students when adults focus on artificially raising the graduation rate instead of making sure that students are learning,” said Burroughs, the board’s vice chairman.

Burroughs expressed concern for those who did not earn diplomas.

“We need to look at these students and figure out how to support them and learn from their unfortunate experience so we can better prepare our students not just to graduate but to be successful all through school,” he said.

Statewide, the graduation rate fell by about half a point, to 87.12 percent. Ten of the state’s 24 systems slipped, while 14 edged up, but many of the changes were by less than a point. Montgomery County’s rate dipped 1.17 points.