After years of steady improvement, the city’s 4-year high school graduation rate flattened in 2011, according to new figures released by the state today.

Of students who entered high school in 2007, 60.9 percent graduated four years later, according to the new figures. When August graduates are included, the rate rises to 65.5 percent.

Sixty-one percent of students who entered city high schools in 2006 graduated on time in 2010. That year’s graduation rate with August graduates included was 65.1 percent.

The plateau comes after six years of growth that saw graduation rates rise from 46.5 percent in 2005 to 61 percent last year. Before that, graduation rates were stagnant for a decade and its steady improvement over the past six years has been one of the Bloomberg administration’s cornerstone achievements to cite in defending its education policies.

And as graduation standards increase, the flattened figures aren’t likely to resume that rate of improvement in coming years. Graduation could drop by as much as much as 10 percent next year. That’s the percentage of high school students – or about 8,000 students – who graduated with a local diploma, which allowed them to graduate despite scoring under 65 on one Regents exam. The local diploma has been phased out and the option won’t be available to this year’s students.Graduation rate fell slightly for black students – from 60.6 percent to 60.4 percent – and grew slightly for white, Asian and Hispanic students. The city’s college-readiness rate also fell slightly, from 21.4 percent to 20.7 percent.

Most of the state’s other large urban districts saw more significant increases in their graduation figures. Those districts collectively improved by about 6 percent.

As usual, the city will be holding a press conference to offer its take on the graduation data. Just minutes after the state released the graduation data, Department of Education officials posted a slideshow presentation that highlights some of the city’s gains. For instance, a higher rate of students are graduating with more rigorous diplomas and graduation rates in the city’s newer schools are significantly higher than the low-performing ones they replaced.

To highlight this growth, this afternoon’s press conference will take place in the old Bushwick High School building, where three smaller schools are now at capacity.