The trial at Nottingham Crown Court heard that the two boys disliked each other.
The 16-year-old told the court he was annoyed and upset after hearing Luke had been passing notes to his girlfriend.
Scare
He claimed he had only intended to scare Luke and not to harm him.
Tests revealed Luke died from a single stab wound to the heart.
Luke's headteacher said: "We have all struggled to understand how this could have happened in our small rural school, where violence is a rarity."
Memorial
A memorial fund for the schoolboy has raised at least £40,000. Luke was an excellent sportsman and the cash is likely to be spent on a sports facility for the community.
Meanwhile, the local council has announced it is carrying out an inquiry into what happened.
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