Bloomberg Takes Blame Over Chancellor Mess

After 3 Months, Mayor Replaces Schools Leader

The decision to remove Ms. Black represents a rare step by Mr. Bloomberg, who takes pride in standing behind his deputies in the face of public criticism. But it had become increasingly evident that the appointment of Ms. Black, whom the mayor had personally championed, was dragging down his personal popularity, which was already damaged by the city’s difficulties responding to the blizzard that paralyzed New York in December.