City Schools Chancellor Carmen Farina is stepping down after four years on the job.
There will now be a nationwide search for her replacement.
There had long been talk that Farina would eventually step down.
The 74-year-old had just retired from a long career as an educator, when Mayor Bill de Blasio convinced her to become chancellor in 2013.
The latest numbers from the Department of Education show standardized test scores increased in every school district under her watch.
Farina also played a large role in implementing pre-k for all.
"Suffice is to say I asked a lot of Carmen Fariña and she gave me even more," De Blasio said.
"There is nothing more satisfying than being able to be a public servant and really mean it, that you're a servant of the people. And all the statistics, and we could have a lot more that what we heard here today, and we've managed to break ground on so many different things. The thing I'm proudest of is the fact that we have brought back dignity to teaching, joy to learning and trust to the system," Farina said.
Mayor de Blasio says NYPD Commissioner James O'Neill, FDNY Commissioner Daniel Nigro and Corporation Counsel Zachary Carter will be staying in their roles through the mayor's second term.