Bloomberg with Walcott and Nilda Gomez-Katz, one of four high school principals at the old Bushwick High School building.

Mayor Bloomberg did his best to put a rosy spin on the newly-released graduation rates that showed New York City’s progress last year has flattened for the first time in seven years.

Stunted graduation numbers weren’t a setback as much as they were an impressive achievement in the face of higher standards, he said at a press conference this afternoon. And better rates of improvement in other cities weren’t an indication of New York City’s failures, but a credit to what those school districts were doing right.

“They’re doing a great job and they should be congratulated,” Bloomberg said, even though in past years he’s used such comparisons to tout his own city’s growth. “That doesn’t mean we aren’t doing a great job.”

But even Bloomberg grew sober when asked about future graduation rates. Beginning this year, all students who began high school in 2007 or after will not have the option to earn a less-demanding local diploma, which for years helped prop up the city’s overall graduation numbers.

“That’ll make it tougher,” the mayor said. The man to his left, Chancellor Dennis Walcott, quickly agreed.

Last year, about 10 percent of the city’s graduates earned a local diploma, which was available to students who scored between 55 and 65 on the New York State Regents exams. That won’t be an option this year, meaning graduation rates could drop significantly.

The elimination of the local diploma is part of a larger effort to make students more prepared for college, but critics have said it will leave thousands of students at risk of dropping out.

Officials played down those concerns on Monday and said that demanding graduation requirements was more important than four-year graduation marks.

“If you raise standards, it is going to be tougher to get everybody up to the same level,” Bloomberg said. “But we’re in favor of raising standards.”

Walcott said he didn’t expect dropout rates to increase if students can’t meet the graduation requirements in four years. If anything, he said, the city would focus on efforts to keep them in the school system until they complete their graduation.

Graduation rates could fall for other reasons, as well. As part of new guidelines being implemented next year, principals are required to limit the controversial practice of credit recovery, a program that allows students to quickly earn class credit through online work. The guidelines will also prohibit teachers from grading their own students’ exams, which experts believed led to inflated test scores.

Chief Academic Officer Shael Polakow-Suranksy said he expected principals could successfully meet the new guidelines without sacrificing graduation rates.

“We’re confident that, in the data that were seeing, people are rising to the challenge,” said Chief Academic Officer Shael Polakow-Suranksy.

The press conference took place in a classroom belonging to the Academy of Urban Planning, one of four small high schools that replaced the now-closed Bushwick High School. Bloomberg used the opportunity to highlight the differences in graduation rates between low-performing high schools and the small schools that replaced them when they closed. In 2002, the 19 large high schools had a combined graduation rate of 35.7 percent, while the small high schools that replaced them stood at 68 percent in 2011.

But even parts of those numbers were disputed. The United Federation of Teachers emailed reporters a graph showing that the graduation rate of more than 100 new small high schools had dropped significantly from 77 percent to 69 percent in the last five years.

DOE officials quickly sent over what they said was a more accurate graph of the same schools. Graduation rates have declined from 73 percent in 2009 to 70 percent last year, according to the DOE’s version.