A parent chaperone punched a seventh-grade girl during a choral concert at MS 51 in Park Slope on Friday night, and school administrators let the woman leave without calling the police, the girl's mother claims. The 13-year-old was backstage with a group of 40-50 students around 7 p.m., and was waiting to perform in the final night of the three-day spring choral recital. She opened her mouth to spit out some gum, and the chaperone, Roberta Woelfling, came over from across the room, scolded her about sticking her tongue out, walked away, then came back and punched her in the mouth, according to her mother, Petal Joseph.

Joseph is upset about the alleged assault, but she is just as upset about what happened next. Her daughter ran to an assistant principal and told her what happened, and the assistant principal and security guards let Woelfling leave the building, didn't notify Joseph, and sent the girl back onstage to perform. From the audience, Joseph said she saw "my child's demeanor had completely changed from when she was on stage the first time," and that the girl was "physically shaken." (A statement written by the assistant principal that night and provided by Joseph also describes the girl as "visibly shaken.") But Joseph says she didn't know what happened until the performance ended and her daughter came to her, unaccompanied, and asked, "Mom, did they tell you what happened?"

The girl gave a statement to the assistant principal that night, writing, "I want [Woelfling] to get arrested and get charged and go to jail for what she did to me."

Joseph went to the police the next morning, by which time her daughter's lip had swelled, but she said officers told her they were reluctant to file assault charges because there was no serious injury. School administrators didn't meet with Joseph and Woelfling until Monday morning.

"I can't even believe this whole situation has happened, and I can't believe the whole story that this woman was allowed to concoct, the hours that she had to think about what she did," Joseph said. "And it's really upsetting that I sat in that audience for two hours and was unaware that something had happened to my child."

Woelfling, an architect, denies punching the girl. She said that she did tell her that it's disrespectful to stick her tongue out, and flicked the back of her fingers in the direction of the gum, but that the girl "turned at that exact moment, so my two fingers touched her face."

"It wasn't a hit and a beat. It was an accident," Woelfling said. "It wasn't intended to touch her mouth, her gum, her tongue. It was something that has been blown out of proportion."

Woelfling faulted Joseph for "ramping it up" and stressed that she is the opposite of a child abuser.

"I'm the type of parent that volunteers for everything. Nobody wanted to volunteers for this," she said. "It's a tough gig trying to keep kids in line."

Woelfling said that she didn't flee the building after the incident, an administrator told her she had to leave. Police have not arrested Woelfling, but Joseph is demanding that they do so, and told us her daughter was being interviewed by police this morning. Joseph also said she is talking to lawyers about a potential lawsuit against the school for its handling of the situation.

A Department of Education spokesman said only that it is investigating, and the principal and two assistant principals at MS 51 did not respond to repeated requests for comment. The Fifth Avenue school is connected to some of the most powerful people currently in city government. It is where both of Mayor de Blasio's kids went to middle school, and it is where he announced the appointment of Carmen Fariña to the post of Education Department chancellor. She served as the superintendent of the neighborhood's school board during the 2000s.

Joseph said that, as upset as she is, the incident shouldn't be taken to reflect on the whole school.

"I love the school," she said, "but this incident and this particular woman needs to be addressed."