Administrators responded by canceling all of next week's activities.

Formerly known as Akiba Hebrew Academy, the school moved last year from Merion to a 35-acre campus in Bryn Mawr.

The school's 55 teachers have been working without a contract since Aug. 31, said Jared Freedman, a spokesman for the Jack Barrack Teachers Association, Local 3505.

"It's sad the strike had to come about," Freedman said. "But it wasn't what we wanted to do to improve the contract. It's because of what they wanted to take away from us."

Freedman said contract talks reached an impasse over pensions.

"We had expected having to pay more into our medical plan and not taking a pay raise in the first year, which in these days is unheard of," Freedman said. "But the one thing we thought they'd never take away from us was our pensions."

The head of school, Steven M. Brown, declined to comment yesterday.

Earlier yesterday, administrators distributed an e-mail announcing all classes and extracurricular events were canceled from Monday through Friday.

"We have offered our faculty as generous a compensation package as our stretched finances permit," Ariele Klausner, president of the school's board of directors, said in a statement. "Unfortunately, the association's compensation proposals far exceed our ability to fund them, and we have been unable to reach a settlement at this time."

The teachers' association had settled for smaller salaries in previous contracts in return for the school's matching up to 7 percent of each teacher's pension fund contribution, Freedman said.

During contract negotiations this year, school management initially sought to eliminate the matching funds.

"They originally said they were taking back all the matching funds for the first two years," Freedman said. "Since then, they've come up a little bit, but not to where we have to be."

Freedman said the school was having financial problems since the move to Bryn Mawr.

"Nobody told them they had to buy a new facility," Freedman said. "They claim that fund-raising is not going as well as it should go. But they shouldn't be trying to make up the difference on our teachers' backs."

The school has 315 students in grades six through 12. According to its Web site, upper school tuition was $22,850 for the 2008-09 school year.