Prince George's County officials said they welcome the probe and reiterated that there were no orders from the top to do anything improper.
"We've said all along there is no effort by my administration or myself to tell people to cheat, to do things wrong," schools chief executive Kevin Maxwell told reporters. "Do we have some people that haven't dotted I's and crossed T's, or not followed all the directions they were given? Undoubtedly, in an organization with over 20,000 employees. But that doesn't make it a systemic issue."
The examination begins two months after the Maryland State Board of Education voted to bring in an independent investigator to review allegations of fraud in the 132,00-student district, the state's second-largest.
Gov. Larry Hogan (R) asked the state board to investigate in June after a four-member minority bloc on the Prince George's school board alleged that whistleblowers had come forward with evidence that grades were changed and that hundreds of students had graduated without meeting state requirements.
Edward Burroughs III, the leader of the minority bloc, said the involvement of outside investigators is important, allowing employees to come forward "with the comfort of knowing their identities will be protected" if they make disclosures.
"At the end of the day, we hope that justice is served," Burroughs said. "Corruption should have no place in our county and especially in our school system."
State education officials said Alvarez & Marsal has extensive experience in audits and has done work identifying fraud and data manipulation in educational environments.
They noted that the state board, which oversees whether local school systems comply with graduation requirements, will make a final determination on whether rates were accurately reported after reviewing the report from Alvarez & Marsal.
State data shows that four-year graduation rates in Prince George's improved from 74.1 percent for the class of 2013 to 81.4 percent for the class of 2016, the largest uptick for that time period of any school system in the state.
Maxwell, who was appointed by County Executive Rushern L. Baker III to a second term this year, has touted graduation rates as a key accomplishment and has called the allegations of fraud politically motivated.
Appearing with Maxwell on Tuesday, Baker (D) said officials would take action against any school employee found to have acted fraudulently.
"That's unequivocal," he said. "We believe the investigation will show that there is nothing that is systemic throughout our system but where there are charges, where there are things that have gone wrong, those people will be dealt with."
State education officials looked into graduation rates in Prince George's last school year, following an anonymous complaint to federal officials, and found no evidence of wrongdoing. But critics have said that investigation was limited and not sufficiently impartial.