"The boy, who is also a minor and studying in class 12th attacked the girl with a sharp-edged weapon and stabbed her in the neck," said Police inspector M M Vasava.
The incident took place in the Siddheswar Patia area when the girl was returning home from the school.
The girl, a std 10th student, died on the spot.
The youth was courting her for the last six months, police said. He is still to be traced.