It has long been considered a steppingstone to prestigious private schools and elite colleges, even if its pupils are barely out of diapers.

But the Park Avenue Christian Church Day School, an exclusive prekindergarten on the Upper East Side, will not be sending as many boys and girls down that privileged path this school year.

About 30 families have withdrawn their children after learning -- in the waning days of summer vacation -- that the church planned to sell the school's building to a developer and that the school was moving to the Upper West Side.

"It's incredible and unprecedented, for sure," said Roxana Reid, an educational consultant who advises parents on how to get their children admitted to New York's private schools, including Park Avenue Christian. "There's been a history of consistency that the school has enjoyed for many years, and this really upsets the balance."

Parents have taken to Urban Baby and other Web sites to express their dismay at both the school and the church's leadership. Some noted that they were not told of the move until after their tuition checks -- for $20,000 -- had been deposited and when it was past the point, realistically, to apply to other preschools.

One parent called the church's actions irresponsible and deceptive. She asked, as others did, to remain anonymous for fear of jeopardizing the chances of getting a tuition refund and added that many parents felt duped.

Park Avenue Christian Church, which is affiliated with the Disciples of Christ, wants to sell its five-story annex, at 1010 Park Avenue at 85th Street, which houses the school, to raise money for its small congregation, according to church officials.

The prospective buyer, the Extell Development Company, intends to raze the building to make way for an apartment tower, though the deal has not yet been finalized.

Parents complain that the new building, on West 76th Street, just off Central Park West, is farther away from most of the students' homes, is smaller than the current building and does not have a rooftop playground. School officials said that the children would be taken to Central Park instead.

Last spring, Betsy Newell, the head of school, told the staff that the Park Avenue building, which was built about the time the school was founded, in 1963, would be undergoing asbestos removal over the summer and asked them to remove all art supplies and books. Some parents have wondered if that was part of a plan to empty the building. But Ms. Newell said she knew nothing of the church's plans, first reported on the Web site of the Real Deal, until very recently.

"I was surprised, as I am sure you were, to read the news reports this week," she wrote in a letter posted on the school's Web site.

Ms. Newell did not return several telephone calls or respond to e-mails requesting comment.

The church, which has had about 100 people at its Sunday services over the summer -- about half the enrollment of the school -- apologized for the awkward timing but said the sale of the annex was necessary to ensure Park Christian Church's survival.

"It has always been our mission to bloom where we are planted, and this plan for development helps us do that," the senior pastor at the church, the Rev. Alvin O'Neal Jackson, said in a statement.

A church spokesman, George Arzt, added that the church was reluctant to disclose the sale until members of the congregation had approved it by a vote, which did not occur until Sunday.

Still, Mr. Arzt, who also does work for Extell, acknowledged that the church had signed a contract with Extell to sell the property last year. No price was provided. City building permits, filed at the beginning of this month but not yet approved, are for a 16-story residential tower that will be a $50 million project.

Few obstacles, if any, seem to stand in the way of the project. The site is not in a historic district, which would require additional approvals, and the church buildings themselves are not landmarks.

In an unusual arrangement, however, Extell agreed to a last-minute request by the city's Landmarks Preservation Commission not to alter the church itself, which dates to 1911 and features Tiffany windows, without a thorough review.

In the meantime, work continues to prepare the school's new home, which is in the back of the Fourth Universalist Society church. Classes are supposed to start on Sept. 12, though the space still requires a few city permits before it can be occupied.

The Park Avenue Christian Church said it was paying for the renovation and rent on the building, at 4 West 76th Street, and that it was also looking for a permanent home for the school on the Upper East Side. Mr. Arzt said, however, that the lease for the space on West 76th Street was for five years.

Parents who have requested tuition refunds were to start receiving them this week, Mr. Arzt added, with all reimbursements to be made by early November.

In a 2011 mission statement, Mr. Jackson provided some indication that a major change was at least being contemplated: "We must also determine the real cost of running the day school and review the space limitations imposed by having a school on our premises," he said then.