Police and trading standards officers teamed up to carry out test purchases at pubs in Buxton and Glossop.
Throughout the evening on Saturday, November 15, licensing officers visited nine premises around the town centres as part of a test purchase operation.
The team praised eight out of the nine pubs visited which passed the operation and complied with the sale of alcohol regulations.
A fixed penalty notice of £90 was issued after alcohol was sold to the underage volunteers at a pub in Glossop.
The pub will be placed on an action plan which will see officers working closely with bar staff to ensure that the correct training and procedures are in place.
Sergeant Phil Bateman, of Derbyshire police, said: “It was really pleasing to see that the majority of the licenced premises that we visited passed the test purchases. They operated by the Challenge 25 protocol, asked for ID and refused to serve the underage drinkers.
“Although one of the premises did fail the test, we will work closely with them to offer support and to make sure that they are aware of the rules around underage drinking and that they are confident in checking identification.
“We will be carrying out follow up checks over the next few months to ensure that the correct procedures are being followed and we also welcome any intelligence around pubs that are selling to underage people.”
Test purchase operations are regularly carried out throughout Derbyshire and similar checks are being planned for the future.