The teenagers were kicked out of the Year 12 formal at an Albert Park function venue on April 15 after they were busted with drugs, reportedly including ecstasy.
The school later moved to expel one of the students, and suspend two others, after an investigation confirmed venue security found the students with “illicit substances”.
It has been reported one teenager had ecstasy, marijuana and alcohol and another was caught with a “significant” number of pills, but the school has not confirmed what drugs were uncovered.
On Monday evening, Victoria Police said the trio had all received formal cautions at the weekend.
“Each girl attended with their parents and were cooperative and engaging,” a police spokeswoman said.
The formal cautions mean the three students will not have their involvement in the incident publicly recorded.
“It’s a formal alternative in prosecution of minor cases. It’s like a warning,” the police spokeswoman said.
Melbourne Girls Grammar, in South Yarra, is one of Melbourne’s most expensive schools with fees of $32,736 a year for grade 11 and 12 students.
Principal Catherine Mission said in a statement last week that the two suspended students will be subjected to special conditions upon returning to school.
“The school will be actively supporting these girls once they are back at school,” Ms Mission said.