The incident took place yesterday in the Gandhi Nagar area.
The accused, identified as Vikas, 40, has been arrested, Shahdara’s deputy commissioner of police, Nupur Prasad, said.
The incident comes a day after a seven-year-old boy was gruesomely murdered for resisting sexual assault by a bus conductor in a Gurgaon school, which sent shock waves across the country.
Vikas had been working in the school for the last three years. Previously, he worked as a security guard in the same school, the police said.
The accused allegedly took the girl inside an empty class room in the afternoon when he was walking on the corridors after handing over lunch boxes to teachers, the police said.
After raping the girl, he allegedly threatened her of dire consequences, they added.
The matter came to light after the girl complained of bleeding and pain in her private parts to her mother. She was taken to a hospital where her medical examination confirmed sexual assault, the police said.
Traumatised by the incident, the girl was sent for counselling.
Vikas was arrested after he matched the description of a “man wearing a cap” and other details given by the girl during counselling.
The murder of the seven-year-old boy on the previous day took place at the Ryan International School in Gurgaon, where he was found with his throat slit in the toilet.
A knife was found beside the body.
Several parents protested at a police station and demanded action against the school.
(With inputs from PTI)