During the 1960s and 1970s, after ownership of the site had passed to Kingsmill's daughter Diana Kingsmill Wright, the island was used in a Quaker programme for training in nonviolence, and also as a co-operative conference centre. In August 1965, the island was the scene for a role-playing exercise — later referred to as "the Grindstone Experiment" — in nonviolent social defence.
During the 1960s and 1970s, after ownership of the site had passed to Diana Kingsmill Wright, the island was used in a Quaker program for training in nonviolence, and also as a cooperative conference center. In August 1965, the island was the scene for a role-playing exercise — later referred to as "the Grindstone Experiment" — in nonviolent social defense.