A school accountability era in New York City is going out not with a bang but with a technical briefing in the basement of the Department of Education’s headquarters.

That’s where Deputy Chancellor Shael Polakow-Suransky will be unveiling this year’s progress reports, the letter grades that the Bloomberg administration awarded annually to schools since 2007, to reporters. The setup is similar to what has happened in the recent past but a far cry from the early years of the progress reports, when Mayor Bloomberg and Chancellor Joel Klein used to tout the scores — and their improvement from the previous year — with great fanfare.

The letter grades are not the biggest school story today for Bloomberg and his current chancellor, Dennis Walcott. They’re appearing together early this afternoon at a high school in Hell’s Kitchen to announce a donation from AT&T to fund a new software engineering curriculum.

Mayor-elect Bill de Blasio has said he wants to overhaul how schools are assessed, so today’s grades could well be the last that schools receive, at least under the current system. What they show will become a lasting data point in Bloomberg’s education legacy, along with the city’s higher graduation rate and this year’s dramatic test score decline because of the state’s new standards.

We already have one hint about what this year’s progress reports will say. On Monday, Polakow-Suransky said at a panel event that the lowest-performing 15 percent of schools from last year — all of which received “Targeted Assistance Plans” if the department opted not to close them — had come out ahead on this year’s reports. Three-quarters of the schools with the plans saw their grades go up by at least one letter; 40 percent rose by two letters or more, he said. (Those data points are repeated in a report released Monday about how the city supports schools.)

The grades are based on complex algorithms that compare student progress and performance across schools with similar students. Although the formulas have been tweaked every year, the big picture has remained the same: Elementary and middle school grades have been based almost entirely on state test scores, while high school grades factor in graduation rates and how quickly students earn credits, as well. More recently, high school grades have also reflected how well students are prepared for college, based on whether their students are exempt from remedial courses and stay enrolled over time.

This year, high schools are getting more credit for their graduates’ persistence in college than in the past, although graduates’ college readiness still amounts to only 10 percent of each school’s score. For the first time, middle schools’ scores will based in small part on their graduates’ performance in high school, and elementary schools will see for the first time how their students are doing in middle school, although that won’t factor into their progress reports.

The city also changed the way schools are compared so that schools are grouped with other schools that have similar students. Principals had long complained that the city’s old formula compared schools with many high-need students to schools with relatively few, and schools with many high-need students have been more likely to receive low scores.

The Bloomberg administration devised the grading system in large part to give parents more detailed information about their schools and to shift the focus from raw performance to the progress that students make every year, in an effort to make the point that some schools with struggling students propel them forward faster than others. But de Blasio and many others have criticized the reports’ single letter grades for offering too simplistic a view of school quality.

Usually, the city uses the grades to determine which schools to consider closing. This year, because the closure process would span the two mayoral administrations, no schools will be closed. But Walcott said last week that the department would let low-performing schools know that their progress did not meet standards nonetheless.

Online guides to this year’s progress report formulas offer other indications that the department plans to plow ahead with the progress reports even after the end of the year. Principals have been told to expect additional changes, including the incorporation of the middle school student achievement data point into elementary schools’ grades.