Manhattan Borough President Scott Stringer also put out a statement on this, which just landed in my inbox (in addition to the Tweet, which more people will read anyway): 

“I was shocked to hear the Mayor of New York City advocate the firing of half the teachers in our public schools. Those of us with kids in the city’s school system find the thought of 50 students packed into our children’s classrooms appalling. Parents across the city have a right to question the judgment behind such an irrational policy position. This is the same out-of-touch thinking that led to Mayor Bloomberg’s appointment of Cathie Black as Schools Chancellor. “For the thousands of dedicated teachers who make our schools work, I can only imagine the chilling effect of hearing your boss say, ‘I want to fire half of you.’ For Mayor Bloomberg to go even further and disparage the quality of the teachers in our system adds insult to injury. “I call on Mayor Bloomberg to apologize for his ill-conceived remarks and affirm his confidence in the men and women who have dedicated themselves to teaching our children.”

CBSNY: Mayor Michael Bloomberg: If I Had It My Way I’d Dump Half of New York City’s Teachers