The girl, studying in the first standard, was allegedly sexually assaulted twice on October 28 and 29, Additional Commissioner of Police (Law and Order) Alok Kumar told reporters here.
A man, who is "strongly suspected" for the offence, has been detained and is being questioned "thoroughly" with cases booked under Sections 376 of IPC and 5 and 6 of Protection of Children from Sexual Offences Act 2012.
Sec 376 of IPC relates to rape and Sections 4 and 6 of POCSO Act to punishment for penetrative sexual assault and punishment for aggravated penetrative sexual assault, respectively.
He said prima facie the incident took place in the school, which has already been booked for not complying with safety guidelines issued by police to ensure safety of children.
The girl's mother lodged a complaint in the Jeevanbeema Nagar police station this evening, he said.
Kumar said the police would seek the opinion of experts on further aspects of the case. "After proper verfication, we will take a final view on the accused," he said.
The incident comes just five days after an office assistant in a school here was arrested for sexual assault of a three-and-a-half-year girl studying in nursery.
Recurring sexual assaults on minor girls have evoked public outrage and raised questions about safety in schools and their compliance with safety guidelines issued by police.
An eight-year-old girl was allegedly sexually assaulted by her 63-year-old teacher inside her school premises over a period of time. The offence came to light in early August, barely a month after the rape of a six-year-old girl at 'Vibgyor High' school here which led to street protests.