The teenagers from Harry Carlton school in East Leake, Loughborough, get free bus passes for telling their headteacher about badly-behaved pupils.
Sixth-formers are offered pound;30 monthly travel passes under the "bus mentor" scheme, which began last September.
Graham Legg, headteacher, introduced the scheme after complaints from parents and Nottingham City Transport about pupils smoking, getting out of their seats, throwing litter and being noisy.
Nottingham City Transport spends pound;10,000 a month on bus repairs, and most of the damage is caused by school pupils.
Mr Legg said that only a minority of his students behaved badly on the buses and that the scheme has helped enormously.
"When I get complaints from parents now, it usually turns out that the mentors have not been on the bus because of exam commitments," he said.
"A mentor reported a 15-year-old girl who threw a pot of yoghurt down the bus, which went over a number of seats. She said I had the wrong person when I brought her to my office, but the mentor insisted it was her.
"When I suggested the girl do community service, she went barmy but we got her mother on the telephone and she berated her.
"In the end we took the girl to the local bus depot, got her a pair of overalls and she cleaned a whole bus out. She has not been reported since for any kind of anti-social behaviour."
Michelle Greaves, 18, has been a bus mentor since September. One attraction was the free pass.
"I save pound;13 a week going to and from school and if I go into Nottingham at the weekend I save even more," she said.
"We did get called snitches at first but I am a midday supervisor as well, so I was used to that. I know if I was in Year 7 I would want to travel to and from school without any hassle."
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