The incident was reported Wednesday when the victim, a Class 3 student, spoke about her ordeal to her parents who then approached Rohini South police station in west Delhi.
"The victim was not going to her school for a month by making excuses like stomach ache and others. When her parents forced her to go to school, she told them that her school's lab assistant would misbehave with her," Deputy Commissioner of Police Vikramjeet Singh told IANS.
Following the victim's statement the accused Harender,40, was arrested Wednesday and is now in judicial custody, Singh said.
The victim told the police that Harender molested her three or four times.
The school authorities suspended the accused when they got to know about the incident.