Alonso has vowed to seek the harshest sanctions for principals whose schools have illegitimate test scores, saying they are ultimately responsible for what happens in their schools.

George Washington's principal, Susan Burgess, was removed and stripped of her teaching license, though she denied any wrongdoing in an interview with The Baltimore Sun. The system confirmed that Abbottston's principal, Angela Faltz, was removed pending the outcome of an investigation. Fort Worthington's principal, Shailyn Todd, resigned. Faltz and Todd declined to comment at the time.

Gittings protested the removal of Faltz, who is a member of the union's executive board, saying principals should be allowed to remain on the job until investigations are complete. He did not identify the subject of the administrative hearing when he spoke before the school board.

The union leader also asked the city school board to review how it handles anonymous complaints, because sometimes the complainants can have "vindictive motives." He added that the reports can cause turbulence in a school, as investigations can take up to 18 months.

At least one city school board commissioner, David Stone, agreed with Gittings.

"It is something this board should look at again because it's very disruptive to schools and can be distracting from the real work of teaching and learning," Stone said.

Alonso said any allegation requires the system to investigate. The system receives numerous reports every year from anonymous sources, many who fear retribution. Alonso added that the system does not remove principals based solely on anonymous complaints.

"In the area of testing investigations, every authority asserts that we must, categorically, investigate all allegations, even if anonymous, and we do so," he said. "The integrity of the school system demands that we do so, even if it proves difficult or harmful to individuals."

The schools chief has prided himself on being transparent about the system's challenges with testing integrity, and the district's recent efforts to crack down have been lauded as unprecedented in Maryland and the nation.

Tisha Edwards, the school system's chief of staff, joined other experts at a recent national testing integrity symposium in Washington and said the system's biggest challenge is finding who was responsible for the cheating. She also advised districts to prepare for litigation in their quest to do so.

"Once you find out there has been widespread cheating, it's a whole other situation to find out who is the culprit," Edwards said. "Schools are families, and once people find out there's going to be high accountability, a lot of the times they backtrack, and that makes it very difficult for us. Unlike [other districts], we didn't have anyone confess."

Joining Edwards on the panel was Robert Wilson, the lead attorney who investigated Atlanta public schools that made national headlines in 2011 for widespread cheating, which led to educators facing criminal charges. He offered insight into what he called "an ugly and disturbing truth."

His team issued a 171-page report, which has been made public, identifying 150 educators, 82 of whom confessed, and detailed the pressures educators faced to keep test scores up.

He gave advice to districts about testing integrity: Keep the testing about students.

"If you take the adults out of it, they have no reason to cheat," Wilson said. "When the tests became about teachers and schools, they had something at stake. Image becomes important."

In Baltimore, few details have emerged about whether more people were involved in the cheating, and their motivations.

The school system denied a request from The Sun last summer for reports detailing its cheating investigations, even if names and identifying information were redacted. The system said releasing the reports could have a "chilling effect" on future investigations, reveal investigative techniques and deny those accused due process.

"To release these reports to the Baltimore Sun," the system concluded, "would be contrary to the public interest."