A girls’ school in south Calcutta was attacked on Tuesday by a mob looking for a male teacher accused of sexually assaulting a six-year-old after luring her into a room that is not under CCTV surveillance.

The teacher was arrested on the basis of a complaint by the child’s parents, but not before the government-aided school had been singed by mob fury reminiscent of the agitations last year over similar incidents in two institutes.

The violence started with a group of guardians breaking furniture and damaging a computer in the office of the headmistress. The protest snowballed into a full-blown law and order problem when the protesters tried to set fire to a motorbike parked outside the school, suspecting that it belonged to the accused.

Bricks were hurled at the police contingent before a baton charge forced the mob to disperse.

Personnel from three police stations had been deployed to keep the violence from spiralling. A contingent of the Rapid Action Force was requisitioned, too.

“We want the school authorities to hand over the accused to us. We will teach him a lesson. The school and the police are trying to protect him. The police beat us up because we were protesting the crime,” said the mother of a girl who studies in that school.

The school in the middle of the storm is not being named in accordance with a clause in the Protection of Children from Sexual Offences (Pocso) Act, 2012, that prohibits revealing information that could lead to the child being identified.

“Nothing could be more tragic (than the student being sexually abused by a teacher on the campus), if indeed the allegation is true. The accused has been arrested and an investigation is underway. But the way the guardians protested is unfortunate. This trend of taking the law into their hands is setting a bad precedent. I wonder what the kids will learn, witnessing the unruly behaviour of their guardians,” the headmistress said.

According to the mother of the child, the alleged incident of sexual abuse happened on September 26 in one of the four rooms in the school building that do not have CCTV cameras.

Asked why she took two weeks to lodge a complaint, the mother said: “I had been hospitalised for treatment of dengue and returned home only on Monday. I decided to visit the school after my daughter said she was scared of going to school. She then told me what happened on September 26.”

The woman said she was narrating to the school authorities what her daughter told her when she heard a protest brewing outside.

The headmistress said she heard out the mother of the child who was allegedly attacked but didn’t receive any written complaint.

The police have started a case of aggravated sexual assault and criminal intimidation against the accused. A separate case has been registered against the mob that stormed the school on Tuesday.

“Based on the child’s statement, the accused took her to an empty classroom, made her sit on his lap and sexually abused her. Her father has mentioned in the complaint that the teacher threatened to put a knife into her stomach if she revealed anything to her mother,” said an officer at Lake police station, which is investigating the case.

Kalyan Mukhopadhyay, the deputy commissioner of police (southeast division), said the accused would be tried under the Pocso Act.

Ananya Chatterjee Chakraborti, the chairperson of the West Bengal State Commission for Protection of Child Rights, said the manner of the protest by a section of guardians was unacceptable.

Education minister Partha Chatterjee said the attack on the school was by outsiders. “Those who are not associated with the school are the ones who ransacked the property.”

He said the allegation about sexual abuse of a child on the campus would be probed. “We have asked for a report from the school.”

Teachers of both the primary and day sections of the school were afraid of returning home on their own after the violence. The police later arranged four vehicles to escort the teachers till a particular destination.