Public Advocate Bill de Blasio wrote Mayor Michael Bloomberg Wednesday to ask him to halt school closures and the practice of putting multiple schools in the same building.
The city has targeted 26 schools it wants to close or phase out for poor performance.
In his letter, de Blasio is calling for a one-year moratorium on school closures and so-called co-locations.
He says the school closing strategy fails to provide sufficient support to the highest-need schools.
The letter reads in part, "After years of seeing disruption instead of progress, disparity instead of equity, I write today urging you to halt these policies for the duration of your time in office."
De Blasio says he has repeatedly brought his concerns to the mayor's attention but has been ignored.