The incident took place on Saturday when the accused, Sonu Kanaujiya, lured the girl to the terrace during lunch-time and molested her, police said.
On reaching home from school, the victim revealed the incident to her mother following which on Sunday the family registered a complaint with the police, they said.
A case was lodged against the accused under Protection of Children from Sexual Offences Act (POCSO). He was arrested by the police and after interrogation sent to police custody.