Police sent teenage volunteers into 12 shops in Sheffield to check that staff were not selling alcohol to underage customers.
The children attempted to buy alcohol from shops in the south east of the city but only one teenager was served.
Inspector Jason Booth said: "We conducted a test purchase operation around alcohol sales.
"Our under age volunteers visited 12 premises and only one sold alcohol to our volunteers.
"We will now work with other partners and the premises to ensure this does not happen again.
"Further sales may result in a licensing review."