This is the view of Lord Warner, board chairman.
The decision to remove more than 170 young prisoners from Ashfield followed a damning report by Anne Owers, chief inspector of prisons. She found that Ashfield was "failing, by some margin, to provide a safe and decent environment".
The board could not withdraw young people from the prison without the purchaser-provider relationship that now exists between the board on one hand and the prison service and private sector operators on the other, said Warner.
"The management at Ashfield had several goes at putting things right, but in the end we decided enough was enough. Owers' report was an appropriate opportunity to say that."
He added that in other cases, such as Feltham in London, the board had managed to drive significant improvements. The board has also decided to no longer use Holloway women's prison to accommodate girls.