A woman aged 20 sat as the judge, assisted by a 15-year-old schoolgirl, with the boy acting as the jury.
A number of other young people were present as the mock trial was conducted in the alleged victim's bedroom, the court was told.
Events got out of hand after a group of young people gathered at the alleged victim's home in Trowbridge, Wiltshire, last April.
The girl was sexually harassed and eventually agreed to have intercourse with a man. When she then refused to have sex with the 16-year-old, a mock trial was ordered, culminating in the alleged rape.
The 20-year-old woman and the 15-year-old girl deny aiding and abetting rape. The boy denies rape.
The trial continues.