NEW YORK -- Two Manhattan ninth-graders were arrested Wednesday after a stool tossed from a high school window struck a pregnant woman in the head, school officials said.

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Stool From HS Window Hits Woman

Rosaura Beristani, 29, remains hospitalized in serious but stable condition at Bellevue Hospital on Thursday, officials said. She told doctors she was seven months pregnant, hospital spokesman James Saunders said.

Beristani underwent emergency surgery Wednesday at Bellevue Hospital for head trauma. Officials say her unborn child was unharmed during the incident. She also has a 5-year-old daughter.

Police said the two 15-year-old students face second-degree assault charges.

Beristani, of the Bronx, was taking a break from her job passing out fliers near Washington Irving High School, an eight-story brick building just east of Union Square, when witnesses heard a thud and saw her collapse on the sidewalk.

"She went down very fast," said real estate broker Robert Morrison, who had been meeting a business associate across the street. "Blood was profusely coming out of the side of her head."

Police said a group of students was "horsing around" in an empty social-studies classroom before the stool -- with a wooden seat and metal legs -- was tossed.

Schools Chancellor Joel Klein declared the incident "unacceptable," in a statement released Wednesday afternoon.

Students and workers in the neighborhood of cafes and low-rise apartment buildings said objects often were tossed from the windows of the high school, which has 2,775 students.

"When I walk by here, I always walk on the other side of the street," said Gloria Foti, an administrative assistant at another school down the street.

She said a friend who worked at Washington Irving had warned her to stay off the sidewalk underneath the school windows.

A telephone hung in the branches of a tree near the spot where Beristani was struck.

"They used to throw out glass bottles, books, notebooks, all type of stuff," said Nathaniel McCloud, a 15-year-old sophomore.

According to the school's principal, Department of Education spokeswoman Margie Feinberg said, the last time an object was tossed from a school window was in December, when a book was hurled out.

She said locks at the bottom of windows should prevent objects from being tossed.

The last teacher to use the classroom faces disciplinary action, Feinberg said. Rules require the classroom to be locked if it is not scheduled to be used immediately.