Oprah Winfrey set up the school after a request from Nelson Mandela
A former matron at Oprah Winfrey's school in South Africa has pleaded not guilty at the start of her trial for allegedly abusing students.
The six teenage alleged victims will testify in private, as the prosecutor said they were "very scared".
Virginia Mokgobo, 28, who worked at the Oprah Winfrey Leadership Academy near Johannesburg, was arrested last year.
The US talk-show host has said she was herself abused as a child and has campaigned against abuse in the US.
The school was opened in 2007 at a cost of $40m (Ł20m).
Ms Winfrey pledged to build the academy after a meeting with former South African President Nelson Mandela six years ago, and personally interviewed many of the South African girls from low-income families who applied for the initial 150 places at the school.
Ms Mokgobo was arrested last year on charges including assault, indecent assault and soliciting under-age girls to perform indecent acts.
Ms Winfrey has described the charges as one of the most devastating experiences in her life, and said she had not renewed the head mistress's contract.
She praised the students who reported the alleged abuse.
"My experience with child predators is that no-one ever, ever abuses just one child," she said last November.
She said that because of the high rates of rape and sexual abuse in South Africa, she had tried to ensure predators would not be able to reach students at the school.