Another teacher said several students had been given grades of 50 percent for a quarter. But a spreadsheet provided to The Sun showed that days after the school year ended, the grades that had been entered by the teacher were changed to 90 percent.

The changes, according to the teacher, ensured the students who had failed received a passing grade for the year.

"It's an unfathomable moral failing to give students A's when they earn low F's," the teacher said. "It creates perverse incentives against real academic achievement."

The Baltimore Teachers Union did not respond to inquiries about the investigation and the debate over the district's policies on grades, promotion and retention.

In 2006, school board members and parents objected to the school system's decision to reduce the minimum passing grade from 70 percent to 60 percent. District officials argued the 70 percent mark was too high and inconsistent with the grading scales of the rest of the state, but opponents said the move would lower standards.

In 2011 a policy took effect that prohibited teachers from giving students less than 50 percent for the quarter. Mathematically, that could mean that a student could miss half of the school year and still pass the class.

The policy is unique among area school districts. Only Anne Arundel County has a similar rule — for schoolwork, not grades.

Anne Arundel policy states that teachers can assign a grade of 50 percent for individual assignments "for which the student made a good faith effort as determined by the teacher, to meet the basic requirements." The policy also states: "If a student does no work on an assignment or assessment, the teacher shall assign a grade of zero."

Anne Arundel officials said they implemented the policy after considering the 50 percent rule for quarterly grades — a highly contested proposal that was rejected.

"There was a pretty vocal contention from teachers during the roll-out, who said that if I give them a 50, then I'm giving them something for nothing," said Bob Mosier, Anne Arundel's spokesman, of the policy that was rejected.

Parents have been equally critical of the automatic 50 percent policy in Baltimore City.

Melanie Hood-Wilson, a former city teacher, former vice president of the Parent Community Advisory Board and parent of two city students, said she understands the policy was created to allow students to rebound from a rough academic period but that it sends the wrong message about responsibility.

"While I think that that's very noble, I know that here are students who are well aware of how low of a grade they can get and be able to recover after a semester," Hood-Wilson said. "And setting up a system that allows students to miss key foundational coursework because they're playing a numbers game enables them to lose, enables the system to lose."

The rationale, said Santelises, who created the policy, is to give students hope even if they fail a quarter.

"Part of the spirit of the 50 [percent] is to actually make sure that, given the diversity of our population, young people still have options and still see themselves as being engaged in the process," she said. "It means nothing if we have high standards and are not supporting young people to meet them."