New York (CNN) -- Cathie Black, the publishing executive turned New York City schools chancellor, is stepping down after three months in office, Mayor Michael Bloomberg told reporters Thursday.
"This has not worked out as either of us has hoped or expected," Bloomberg said.
Once dubbed the "First Lady of American Magazines," Black was appointed the city's first female schools chancellor, but was criticized by opponents who were skeptical that her business acumen would translate into effective public leadership.
In her short stint, she oversaw the nation's largest school system, including 1,600 schools, 1.1 million students and 136,000 employees.
She became Bloomberg's controversial choice in November. Black leaves amid a string of recent resignations by high-level city officials.
The former Hearst Magazines chairwoman took the post with a deputy chancellor as her second in command, but she had struggled to build consensus among education leaders.
She will be replaced by Deputy Mayor Dennis M. Walcott, Bloomberg said.
Black replaced Joel Klein, who had held the chancellor's post since 2002 and who entered the private sector as an executive vice president at News Corp.
Klein was the city's longest-serving education chancellor.