Police in Didcot seized dozens of cans and bottle of beer and wine from children in just one afternoon, some of it as they left school.
Officers confiscated the alcohol from more than 100 pupils spotted drinking in their school uniforms last Friday.
Nearly all of them were believed to be 16-year-old Year 11 pupils from St Birinus School, in Mereland Road, and Didcot Girls' School, in Manor Crescent, marking the end of lessons before they take GCSE exams.
Almost 170 cans and bottles of lager, 14 cans of cider, two bottles of wine and three bottles of alcopops were seized from about 60 teenagers at Ladygrove Mounds, the town's skate park, Edmonds Park and even the school gates.
Pc Chris Ball, of Didcot police, said: "We just started taking booze from the school gates and some of them had hidden it under bushes around the town, I understand, so we just went up and took it off them.
"Most of it was seized between lunchtime and 7pm. It was just a one-off but it shows they're getting the booze from somewhere.
"I have never seen anything like it in just one day - it was very unusual."
The headteacher of Didcot Girl's School, Paula Taylor-Moore, said: "I think a staff member saw them in town and called the police.
"The point is girls were seen in Didcot with lots of beer, which they clearly bought from local shops, so someone is selling teenagers alcohol.
"It's these people who should be stopped.
"We had no problems whatsoever during the day and to my knowledge no alcohol was in school.
"It was only a very small minority who took their celebrating a bit too far."
Chris Bryan, the head of St Birinus School, described the incident as a worrying trend but said an overwhelming majority of the Year 11s were not involved.
He said: "We have a close working relationship with the police and we support the action they took and commend them for it.
"What was surprising was it was being done so publicly and clearly young people shouldn't be surprised by the action the police took."
ActiveTen20, an organisation which supports young people, has two alcohol projects running at the girls' school, helping 24 teenagers.
Spokesman Jamie Miller said: "Alcohol is a massive issue in our communities and it seems to be a problem that's getting more out of control. It seems to be more acceptable to young people than it has been in the past."
Police are making increasing numbers of seizures from underage drinkers.
They seized more than 530 litres of alcohol from teenagers during an eight-day crackdown across the county during the February half-term.
Officers confiscated 838 pints of beer, 24 pints of cider, six bottles of wine, 10 litres of vodka and other spirits, and 77 bottle of alcopops, worth almost £2,000.
A total of 63 pints of alcohol were seized from young people in Abingdon, including a 13-year-old child, in March.
During a five-day operation, police officers confiscated just under 23 litres of lager, six litres of cider, 700ml of an alcopop and a bottle of alcohol decanted into a water bottle.
They discovered 880ml - the equivalent of two cans of lager - on the 13-year-old child in Peachcroft Park.
Last month, they seized 23 bottles and cans of lager, 11 bottle of alcopops, three bottles of wine, four bottles of vodka and two bottles of vodka and coke from underage drinkers at a birthday party in Bicester.
Acting on a tip-off, police had raided a 16th birthday party at Bicester Town Football Club.
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