Police have said they are encouraged by results of test alcohol purchases in Leicester despite two bars serving an under-age girl.
Officers targeted A-Level results night on 19 August which is often associated with a surge in illegal drinking.
Of 22 bars and clubs approached, two refused the 13-year-old entry and 18 refused to sell her alcohol.
Each person who made a sale will now be interviewed and could receive an £80 fine, police said.
Pc Jon Webb, an officer from the Neighbourhood Action Team in the city centre, said: "This time we purposely conducted the operation on A-Level results night, knowing that there could be a large number of underage drinkers in the city.
"The results show that the message is getting across, but it's still concerning that two members of bar staff failed to request identification and served the 13-year-old girl."