Three Walt Whitman High School students apparently skipping class a week ago lured a woman from an escort service to a house in Bethesda and then beat and sexually assaulted her, according to Montgomery County police.

A 14-year-old ninth-grader was arrested at the Bethesda school yesterday morning. His identity is being withheld because he is a juvenile. The other students, 15-year-old Andrew Klepper and 19-year-old Young Song, were arrested off campus Thursday and charged as adults with multiple counts.

The alleged attack took place Nov. 8 at Klepper's home in the 7900 block of Quarry Ridge Way. Officer Derek Baliles, a police spokesman, said the teenagers contacted the 25-year-old "adult entertainer" through an Internet ad and posed as adult video producers who wanted to offer her employment.

When the Gaithersburg woman walked into the house shortly before noon, the trio hit her in the head with a bat, took her cell phone and keys and threatened her with a knife, police and prosecutors allege. They then ordered her to undress and assaulted her sexually with the bat and another object, authorities said.

She finally was allowed to leave but only after the students took about $2,000 from her vehicle and made her agree "not to report the incident," according to a preliminary police report. Though the woman waited several hours before calling 911, a medical exam concluded that there was physical evidence that she had been assaulted, Assistant State's Attorney Karla Smith said last night.

Klepper, a 10th-grader, has been charged with first-degree sex offense, conspiracy to commit a first-degree sex offense, armed robbery and conspiracy to commit armed robbery. Song, a senior, was charged with armed robbery, conspiracy to commit armed robbery and first-degree assault.

Both spent Thursday night at the county jail and appeared via video for brief bond reviews yesterday before District Judge Patricia Mitchell. Dressed in green jail jumpsuits, neither commented about the incident during their appearance, Smith said.

Mitchell denied the state's request for Klepper to be held without bond, and he was released after his parents posted a $50,000 cash bond. Song's review was continued until Monday, and he remained in jail.

Smith was unsure whether the 14-year-old was still in juvenile detention last night.

Whitman Principal Jerome M. Marco said he learned of the incident when the ninth-grader was arrested. Brian Porter, a spokesman for Montgomery County public schools, said he could release no information on the students. "Inquiries are being made as far as the ramifications [of their arrests] on their continued enrollment at school," he said last night.

Klepper's mother, reached at her home, had no comment. It was unclear where Song and the other teenager live.

Staff writer Valerie Strauss contributed to this report.