Just as Superintendent Arlene Ackerman promised, the ax has fallen.

At least six Philadelphia principals will be removed from their jobs at the end of the school year, and more could follow, union officials said yesterday.

The principals of two struggling neighborhood high schools and four elementary schools received letters this week informing them that they would no longer work at those schools, effective at the end of the school year.

They will remain with the district, either as principals or central office staff, said Michael Lerner, president of the principals' union, who said he did not know the reasons for the ousters.

South Philadelphia and University City High principals were informed Wednesday by letter that they were being removed, Lerner said. He declined to name the elementary schools. The district has not notified the union of the personnel moves, he said, so he does not know if there are others.

"I have been told unofficially that these letters are the tip of the iceberg," Lerner said.

District officials said they would not confirm or comment on personnel matters.

The moves came on the heels from a vow by Ackerman that the Philadelphia School District would crack down on principals and teachers - moving, firing, or disciplining many more than in the past. She said the bar for teachers and principals was being raised.

Last year, she said, out of a teaching force of 10,700, 13 teachers were rated unsatisfactory and five were fired. None of the nearly 300 principals was removed because a school failed to meet academic standards.

"There will be changes in the principal staff, and there will be many more teachers who will be rated unsatisfactory this year," Ackerman said in an interview with The Inquirer this week.

Anthony Irvin, principal of University City High School, did not return calls asking for comment.

Alice Heller, South Philadelphia's principal, confirmed that she received a letter saying she would be removed at the end of the year but said she would fight it.

"I'm going to do everything I can to stay at South Philadelphia High School," said Heller, a longtime district employee who has also headed the charter school office. "I think it's in the best interest of the students and the community."

She declined to comment further.

Irvin, brought in as a "turnaround specialist" by the district in 2006, previously worked as an assistant principal in the Coatesville and Colonial School Districts.

Both University City and South Philadelphia are "empowerment schools" - among the district's most struggling schools, given extra support and scrutiny.

In February, Ackerman sent letters to about 30 principals warning them that if conditions at their schools did not drastically improve, they would be removed from their jobs.

It was not clear last night whether Heller and Irvin had received warning letters.

On Wednesday, the ousted principals were hand-delivered letters from their regional superintendents telling them the change was being made "in order to best meet the needs of the students and staff. You will be notified in the near future what your next assignment will be," Lerner said.

Lerner, head of the local chapter of the Commonwealth Association of School Administrators, said that while the district could, under the terms of its contract, reassign administrators, he was troubled by the process.

If principals have the talent to succeed in their positions but are coming up short, they must be given support, Lerner said. If they are not capable of making the grade, they must be given the due process their contract guarantees, he added.

"This administration has come up short on both of those points," said Lerner, who added there has been little support for struggling principals.

He said he took issue with Ackerman's methods.

"Her actions have not measured up to the promises made for transparency, for involvement, for collegiality, for a seat at the table," he said. "I am not looking for a war. I want to work collaboratively with the administration."

That no administrators were removed for poor school performance last year makes sense, he said.

"Ninety-nine percent of my members are doing a hell of a job," Lerner said. "You can't be an urban school administrator unless you have that fire in your belly."

Contact staff writer Kristen Graham at 215-854-5146 or kgraham@phillynews.com.