Sanjay was attacked in Pul Prahladpur while he was returning home from school in the afternoon. One the attackers was his classmate, police said.
He was stabbed thrice on the chest and thigh and he died on way to the hospital.
Police are yet to arrest the attackers.
Police suspect that Sanjay was attacked since he had slapped his classmate for teasing his sister.
The boy studied in Class 11 in a government school.
Photos: Shah Rukh Khan, Shweta Bachchan at Karan Johar's book launch
Photos: Sunny Deol with sons Karan and Rajvir at Mumbai airport
Photos: 10 beautiful moments that capture winter around the world
Photos: Karisma Kapoor, Preity Zinta, Shraddha Kapoor at Mumbai airport
Spotted: Anushka Sharma and Diljit Dosanjh at Mumbai studio