A 14-year-old boy suffered a cut to his face after he was hit by a stone.
The schoolboy was found on Pickup Street in Oswaldtwistle and taken to Royal Blackburn Hospital for treatment.
The injuries were not thought to be serious.
Police said there had been a dispute between the victim and another child of similar age before the stone was thrown.
An investigation is being carried out and no arrests have been made.
The incident happened at around 2.40pm on Monday, January 27.
Anyone with information should call Lancashire Police on 101.