The year group was punished after various pranks were played - which it is understood included fish being left to rot around the school, damage to keyboards and liquid substances poured down stair handrails.
Food brought in for a celebration party at Kilwinning Academy, Kilwinning, North Ayrshire, was donated to a local nursing home after the teens were sent home early.
The head teacher slated the ‘unacceptable’ behaviour and said the school will look at how they handle leavers’ events in future.
Head teacher Tim Swan said: “Unfortunately, the behaviour of the leavers on the day was simply unacceptable.
“We had no option but to send them home to begin their study leave early and cancel the celebrations that were planned for the day.
“We will now look at how we handle leavers’ events in the future.
“We spent most of the remainder of the day clearing up the mess and ensuring the other pupils could have a clean and safe place to learn.
“It was agreed in advance by the pupils that the money from the lockers deposits would go on the celebrations - food etc - and the majority of this has already been spent.
“The purchased food was donated to a local nursing home.”
Cunninghame South MSYP Aaran Mcdonald said: “It was deeply unfortunate that due to the actions of a small minority the last day for the whole of 6th year was ruined - I wish it had turned out differently but it didn’t.
“I cannot and will not condone the actions of those who took pranks too far which led to damage to school property.
“It is however deeply upsetting that those of us who had planned fun pranks and spent money in anticipation of a good and fun day have had our last day ruined.
“I want to wish all sixth years who have left school the best of luck with their future and exams.”