In 1971, Mr. Richard Bradley became the fifth headmaster of Ridley. In September 1973, Ridley became co-educational, and eleven girls were enrolled and assigned to the first floor of Dean's House (which has since reverted to a boys' residence, given that several separate girls' residences were built). Also in 1973, the McLaughlin building was built, which was named after Col. Robert Samuel McLaughlin, who pledged CAN$900,000 from the McLaughlin Foundation. The building housed fifteen new classrooms, the new Matthews Library, a new art room, and a new biology laboratory. Today, the building is still home to the Matthews Library and classrooms. In September 1978, girls began boarding. Also that year, the Griffith Arena was opened.