We were surprised today to learn that Mayor Bloomberg dismissed his hand-picked Schools Chancellor, Cathie Black, after 97 infelicitous days as chief of New York City’s school system. The mayor did not set a speed record, however, in dismissing a commissioner who did not work out.

That distinction falls to Mayor Koch, who took just 74 days to fire Robert J. Milano, whom Mr. Koch had appointed deputy mayor for economic development at the start of his first term in 1978. Milano died in February 2000, and Koch said today that they parted ways because Milano wanted to expand his agency and Koch wanted to shrink it.

Ms. Black was never able to counter the wave of negative judgments that followed her appointment by Mayor Bloomberg on November 9, 2010, a scant hour after the departure of Chancellor Klein, who had set a record for length of service. Mr. Klein was chancellor for more than eight years, Mr. Bloomberg having appointed him on July 29, 2002. Ms. Black also set a record, for brevity of service.

In general, Mr. Bloomberg has been praised for the quality of his appointments to high city positions. He has a committee on appointments, led by the highly respected former deputy mayor (under Koch) Nat Leventhal. The Black selection was out of character and did not follow the normal pattern of vetting potential candidates. It is suspected that the mayor was more than willing to dispense with the services of Mr. Klein, whose luster had been dimmed by federal statistics indicating that the academic achievement of New York City students was not as great as Mr. Klein had led New Yorkers, including perhaps the mayor, to believe.

The beleaguered mayor deserves some credit for firing Ms. Black before she became a further embarrassment. He showed that he could dismiss his own appointees, even if that leads to the conclusion that he made an error in hiring them in the first place. It should also be pointed out that although this is the tenth year of his mayoralty, it is the first time that such an inappropriate appointment was made, and he corrected it on his own.

We were highly skeptical of the Black appointment from the start, and wrote about it twice. On November 10, we wrote, under the headline, “Klein Out, Black In. Does She know How To Teach the 3Rs”: “One would imagine that if one were seeking to fill the most important school superintendency in the United States, some person could be found who was both a brilliant manager and had some experience in public or private education. The appointment was not required to have been announced within minutes of the news of Joel Klein’s resignation to enter the field of publishing.”

On November 12, under the headline Prospects Dim for a Waiver on Nominee as N.Y. Schools Chief, we wrote:“No truly independent screening panel of educators is likely to conclude that no experience whatsoever in their professional field is adequate preparation for the most difficult and complex job in local public education. If they felt that way, they would be expressing the view that their own professional qualifications had little value, and that any corporate executive could fill the positions they now hold…

“It could be said that the chancellor, a person whose importance is comparable to that of the police commissioner, should be a person of impeccable and undisputed credentials, a Horace Mann of the 21st century, if such a person could be found and persuaded to take the job. To select a chancellor with no background whatsoever in education is certainly a daring leap of faith.”

The leap of faith has not led to a happy landing, and the plug has pitilessly been pulled on the publisher. President Kennedy and thousands of others have said that public service is the highest calling, if it is done wisely and well. If it is not, one finds another person to serve. The republic will endure. So will Ms. Black.

The task now falls on Deputy Mayor Walcott. We have known him for many years, and we like and respect him. This will be the most challenging task he could possibly attempt. We hope he succeeds.

One piece of advice for Mr. Walcott: Call Diane Ravitch and Sol Stern. You don’t have to do everything they say, but you should listen to them carefully. They can tell you a lot about the system for which you are now responsible. They are not bound by the mistakes of the past, and neither should you be. There are over a million children out there for whom you should be a great hope. Do everything you can not to let them down.

Mr. Stern, president of New York Civic, is a frequent contributor to The New York Sun.