BILL DE BLASIO had a lot going on last week after his resounding victory to become the next mayor of New York. But we hope he was paying attention to the federal release of student test scores . The places that successfully lifted student performance were those that have been the most aggressive with reform. That should give pause to Mr. de Blasio’s desire to undo some of the changes made in New York City in the past 12 years.

Mr. de Blasio (D), The Post’s Lyndsey Layton and Michael Alison Chandler reported, plans to backtrack on or abandon many of the education policies put in place by outgoing Mayor Michael R. Bloomberg (I). The mayor-elect has said he will impose a moratorium on closing low-performing schools, end A-to-F report cards for schools, rely less on test scores to judge teachers and be less supportive of public charter schools.

It is those very principles — data-driven accountability, school choice, honest evaluation of teachers and compensation that rewards results — that helped fuel the significant growth in student achievement in the District and Tennessee on the 2013 National Assessment of Educational Progress. Other states that exhibited progress on the respected “national report card” — Indiana and Florida, for example — also embraced these basic tenets of school reform, which were pioneered in New York by Mr. Bloomberg and his former schools chancellor, Joel Klein.

Lest anyone forget just how rotten the city’s schools were when Mr. Bloomberg took office and won mayoral control of the system, read the thoughtful analysis Paul Hill, founder of the Center on Reinventing Public Education, wrote last month for the Atlantic. Mr. Hill detailed the increase in graduation rates and the upward trend of test scores, the replacement of failed high schools with better-performing small schools and the success of charter schools.

There’s no question that there are still big problems in the system, and far too many students are ill-served. But that argues for more boldness, not timidity, in tackling the issues. Mr. Bloomberg was blocked in undertaking all the reforms he wanted by unions that resisted any change to the status quo and a state legislature often bound to those interests. Both are likely to be challenges as well for Mr. de Blasio: The unions are already clamoring for billions of dollars in back pay for the years they worked without contracts, and good luck to Mr. de Blasio in getting Albany to go along with new taxes to finance universal preschool.

One Bloomberg initiative that Mr. de Blasio doesn’t plan to undo is mayoral control of the school system, something we, too, support. He will have the authority to run the schools as he sees fit, including making the all-important selection of a schools chancellor. He needs to keep in mind, though, that that also makes him directly responsible for New York’s educational results.