TWO girls who exposed their school principal as a sexual predator say their lives have been ruined since they were expelled from the Christian college.

Friends Sarah Johnson and Bec Gavan blew the whistle on St Andrew's Christian School headmaster Frank Bailey, who is awaiting sentencing after pleading guilty to sex charges.

Expelled for blowing the whistle on a sexual predator ... Sarah Johnson with her parents Brenda and Peter. Credit:Paul Harris

Their warning went unchecked by the Education Department, the Department of Community Services and police from the child protection unit, culminating a month later in the drugging and multiple rape of another teenage girl.

In March, Bailey, 43, pleaded guilty to five counts of sexual intercourse with a person in his care.