The crackdown at two high schools in the Scottish Borders follows an epidemic of underage drinking in the area. Youngsters found to have smuggled alcohol into their parties could even be breath-tested by officers.
Offenders will be removed and parents summoned to take them home.
In one recent incident in Berwickshire, a 15-year-old boy was found drunk and unconscious in the street.
In a bid to reduce such incidents, Lothian and Borders Police will send officers to Christmas dances at Eyemouth and Berwickshire high schools, near Duns, next week.
A spokesman said random tests would use a dip strip. He added: "This is dipped into drink to detect alcohol." Asked if youngsters would be breathalysed, he said officers would have the necessary equipment but its use would depend on circumstances.
Constable Kirsty Nash, who is involved in the operation, said youngsters were "generally receptive" to talks in school about the dangers of drinking.
Alcohol Focus Scotland said: "Any initiative that seeks to raise awareness of the harm that alcohol can cause is to be welcomed."